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UNITED STATES DEPARTMENT OF AGRICULTURE 




BULLETIN No. 329 

Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 




Washington, D. C. 



PROFESSIONAL PAPER 



March 6, 1916 



NOTES ON FIVE NORTH AMERICAN BUFFALO 
GNATS OF THE GENUS SIMULIUM. 

By Arthur W. Jobbins-Pomeeoy, 1 Entomological Assistant. 



CONTENTS. 

Page. 



Introduction 

The adult stage- 

The egg stage 

The larval stage. 
The pupal stage- 



Life cycle and number of generations- 

Insect enemies and parasites 

Simulium as a possible carrier of dis- 
ease 

Bibliography 



Page. 

26 
27 

28 
35 



INTRODUCTION. 

Certain species of the insects known as "buffalo gnats" are im- 
portant enemies of man and domestic animals in the United States 
as well as in other countries. Although the principal area of abund- 
ance in North America is in Canada and the Northern States, out- 
breaks of pests of this group occur as far south as Louisiana and 
Florida. While they are dependent upon running water for develop- 
ment, they make use of very small streams and, to some extent, of 
irrigation ditches, and are consequently found occasionally in con- 
siderable numbers in the drier parts of the country. 

About 20 years ago buffalo gnats attracted great attention along 
the lower Mississippi River. They frequently became so abundant 
that plantation operations were stopped ^on account of very painful 
attacks against live stock as well as human beings. These great 
outbreaks were due to conditions established by the overflow of the 
Mississippi River. The perfection of the levee system has changed 
these conditions so that the outbreaks are less frequent and of greatly 
reduced severity. Nevertheless, these insects are still abundant 
enough to be considered a pest in the Mississippi Valley as well as 
in many other portions of the South. 

The damage done by buffalo gnats results from their painful bites 
and the loss of blood which ensues. When they are abundant they 

1 Resigned Nov. 20, 1914. 
Note. — This paper is of interest to persons living east of the Mississippi River. 
10981°— Bull. 329—16 1 



2 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

sometimes cause the death of live stock. At the present time no cases 
of disease transmission can be attributed definitely to buffalo gnats, 
but there is a possibility that future investigations will show some 
important connection with the transmission of diseases. 

All of these considerations make it advisable to place on record a 
considerable number of observations which will serve as a basis for 
the control of these insects wherever they occur. 

The major part of the biological experiments outlined in this paper 
were carried on at Spartanburg, S. C. The author wishes to ex- 
press his thanks to Mr. A. H. Jennings, under whose direction the 
work was done, to the Thompson-McFadden Pellagra Commission 
for many courtesies received, and to the directors of the Spartan- 
burg Hospital for the generous way in which they afforded labora- 
tory accommodations and facilities. 

THE ADULT STAGE. 

DESCRIPTION OF EXTERNAL ANATOMY. 

The adults of the genus Simulium are usually very small, the 
largest known North American species (S. pictipes) not measuring 
more than 4 mm. in length. They are compact in shape, the head 
being decidedly small in proportion to the rest of the body, and the 
thorax greatly developed and curiously humped. In some species 
the thorax and abdomen are very pubescent, in others almost naked. 
In color the different species vary greatly, ranging from brilliant 
iridescent yellow and various shades of gray to almost black. 

The species of Simulium are holoptic in the male and dichoptic in 
the female. In the female the facets of the eyes have an equal grada- 
tion in size, diminishing somewhat toward the margin. In the male 
the facets suddenly decrease in size along a line extending on each 
side from the antennal socket around to the post-gense, giving the 
lower portion of the eye the appearance of being divided off by a 
suture. In color the eyes are usually iridescent bronze in the female 
and deep iridescent red in the male. Ocelli are wanting in both sexes. 

The antennas are short, moniliform, and 11-segmentecl. In the 
species here dealt with the antennas of the female have the first seg- 
ment short and cup-shaped. The second is longer, the apical end 
bearing a chitinous ring which serves as the point of attachment for 
the third segment, which is nearly the same in length as the second, 
but pedicellate. The remaining segments are nonpedicellate, broadly 
joined. Segments 4, 5, 6, 7, 8, and 9 are subequal. The tenth seg- 
ment is slightly longer. The eleventh is the longest of the entire 
antenna, narrows to a point at the apical end, and bears from two to 
three short, strong bristles. The first two segments are minutely 
pubescent, with a few strong bristles on the apical portion; the re- 



TRANSFORMATIONS OF BUFFALO GNATS. 



maining segments are densely covered with minute pubescence inter- 
spersed thickly with stronger hairs. The antennse of the male are 
similar in structure to those of the female, except that they are 
more slender and have the third segment much 
longer, twice the length of any of the succeeding 
segments, and the tenth segment usually the same 
length as the one immediately preceding it. (Figs. 
1 and 2.) 

The mouth parts are modified in both sexes into 
a piercing beak, somewhat similar to that of the 
Tabanida?. In the male the organs have become 
greatly reduced both in strength and armature, so 
that they are apparently unable to pierce the skin 
of vertebrates. 



DESCRIPTIONS OF INTERNAL ANATOMY. 

Digestive System. 
PI. I, fig. 2. 



Fig. 1. — Simulium 
venustum. An- 
tenna of adult 
female. Greatly 
enlarged. (Orig- 
inal.) 



The following is a description of the digestive 
organs of Simulium venustum. The diverticulum 
of the oesophagus, or sucking stomach (v e), which is sometimes 
described as the midintestine or stomach, and whose function seems 
to be primarily that of a reservoir for blood, is a large membranous 
bag capable of great distention. At its caudal end it narrows to the 
constriction known as the pyloric valve (jp). This 
is the place of attachment of the Malpighian tubes. 
The Malpighian tubes (m, m), which are greatly 
developed in this insect, are four in number and are 
constricted at intervals, with corresponding lobular 
enlargements. They extend from the base of the 
diverticulum to its cephalic end, turning again 
caudad, and ending, as far as can be ascertained, in 
a small blind nodule. They are opaque white in 
specimens which have not fed, or specimens dissected 
on emergence, but show remarkable changes in color 
at various periods after engorgement. Sometimes 
they are pink, sometimes rather brownish, and in 
specimens which have engorged and lived for 40 
hours they become checkered brown with trans- 
parent intervals. 

The ileum (i), which is situated immediately below the pyloric 
valve, is an elongate, rounded intestine, somewhat curved when in 
its natural position. The substance which it contains is invariably 
more solid than that found in the diverticulum, large granules being 
frequently present. 



Fig. 2. — Simulium 
venustum. An- 
tenna of adult 
male. Greatly 
enlarged. (Orig- 
inal.) 



4 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

Toward its caudal end the ileum narrows into what is probably the 
colon (<?), which leads in turn directly into the sacklike rectum. 
This is round in shape, transparent, deeply striated, and capable of 
great contraction and distention. It contains six large oval glands 
(rg), which are somewhat similar to the rectal glands of Stomoxys 
calcitrans L. At its caudal end the rectum contracts into the 
external orifice, or anus (a). 

Female Reproductive Organs. 

PL I. 

The following is a description of the reproductive organs of the 
female of Simulium venustum. The two ovaries (7<9, to) are situ- 
ated laterad of the ileum (i). They are small pear-shaped organs, 
transparent and composed of a thin outer membrane which forms a 
sack. The interior is filled in newly emerged adults with many 
small nuclear eggs. (PL I, fig. 1.) Joining the ovaries to the diver- 
ticulum and the basal membrane of the outer skeleton of the abdo- 
men are large tracheae, which branch many times, finally ending in 
thin threads. The caudal end of each ovary narrows into a tubular 
oviduct (od). The two oviducts join and form the cephalic end of 
the tubelike structure known as the utero- vagina (v). The utero- 
vagina and oviducts lie immediately above the lower end of the rec- 
tum. Leading from the cephalic end of the utero- vagina on the 
right side is a very narrow tube which terminates in a round, bulb- 
like structure, black in color, with a transparent membrane. This 
is the spermathecum (s), whose function is that of a reservoir for the 
spermatozoa injected by the male at the time of copulation. When 
an egg is deposited fertilization is effected as the egg passes the orifice 
in the spermathecum. 

Development of the Eggs. 

The stages in the development of the eggs within the ovaries may 
be described at five different stages, as follows : 

First stage. — The eggs are round, very small, rather transparent, 
and are present in the ovary in large numbers. As a rule they are 
rather indistinct. (PL I, fig. 1.) 

Second stage. — The eggs become denser and generally larger toward 
the oviduct, more irregular in shape with a tendency toward an oval 
form. As a rule they are still somewhat indistinct. (PL I, fig. 2.) 

Third stage. — The eggs are of a perfect oval shape, dense as a rule, 
and of nearly equal development, those near the oviduct possibly 
larger. These latter have a tendency toward a slight bulge on one 
side. The shell has become somewhat denser in appearance, and the 
eggs on the whole are very distinct. (PL I, fig. 3.) 



329, U. S. Dept. of Agriculture 



Plate I. 




Development of Eggs within the Ovaries of Simulium venustum after 
a Blood Meal. 

Fig. 1.— Condition of ovaries corresponding to stage 1 (without feeding); la, single 
egg from same, larger scale. Fig. 2.— Condition of ovaries corresponding to stage 2 
(after blood meal); also internal anatomy of abdomen; ve, ventriculus or stomach; 
m, m, Malpighian tubes; jp, juncture of Malpighian tubes and location of pyloric 
valve; i, ileum; c, colon; rg, rectal glands; od, od, oviducts; a, anus; v, vagina; s, 
spermathecum; to, left ovary; ro, right ovary; t, t, trachea?. Fig. 3.— Condition of 
ovaries corresponding to stage 3 (after blood meal); 3a, single egg from same, larger 
scale. Fig. 4.— Condition of ovaries corresponding to stage 4 (after blood meal); 4a, 
single egg from same, larger scale. Fig. 5.— Condition of ovaries after oviposition; 
5a, large, fully'developed eggs left near oviducts; remainder of ovarv corresponding 
to stage 1. Highly magnified. (Original.) 



Bui. 329, U. S. Dept. of Agriculture. 



Plate II. 




Male Genitalia of Simulium. 

Fig 1 —Genitalia of male Simulium pictipcs: c, c, Claspers; a, a, a, anal plates; am, am, 
arms; 6, 6, basal pieces; st, st, styli; ad, adminiculum. Fig. 2.— Genitalia of male 
Simulium venustum. Fig. 3.— Genitalia of male Simulium jenningn. Fig. 4.— Geni- 
talia of male Simulium bracteatum. Fig. 5.— Genitalia ot male bimuhum vittatum. 
All greatly enlarged. (Original.) 



TRANSFORMATIONS OF BUFFALO GNATS. 5 

Fourth stage. — The eggs are fully as large as those newly laid on 
grass blades, of the same triangular form, very dense, the shell very 
strong, and not differing from eggs just laid, with the exception that 
occasionally they may be slightly smaller. (PI. I, fig. 4.) 

Fifth stage. — One or two large eggs are usually left in the ovaries 
near the oviduct, and the rest of the ovary is entirely filled with the 
typical round eggs of the first stage. This stage is found after 
adults have finished ovipositing, and also in specimens taken actually 
engorging, concerning which more will be said later. (PL I, fig. 5.) 

The Genitalia of the Male. 
PL II, figs. U5. 

The structure of the genitalia of the male shows remarkably con- 
stant specific characters. Their systematic value may be seen from 
the striking differences in the illustration. The determination of 
the species based on color alone is at best unsatisfactory owing to the 
amount of variation in individuals of the same species and fading 
of color in dry mounted specimens. The appearance of the structure 
of the genitalia does not change when the specimens are preserved in 
alcohol, and in dried specimens the original shape can be completely 
restored by the following method: 

The last segment of the abdomen of the male after being re- 
moved with sharp scalpel or needle is placed in 6 per cent potassium 
hydroxid (KOH) and left until the soft parts are removed, the 
chitinous portions remaining intact. The material is then washed 
with water, run through alcohol in the usual way up to 100 per 
cent, transferred to xylol, and mounted in balsam, so as to give a 
direct caudal view as shown in Plate II, figures 1-5. Some of the 
European species have been studied in regard to the genitalia of the 
males by Liindstrom, but nothing has been done so far on American 
species. 

The segments to which the organs of the genital armature are 
attached are collectively designated under the name hypopygium. 
The most prominent organs of the hypopygium are the two claspers 
(c c) and the basal pieces to which they are attached. The claspers 
may be either large, fingerlike, as in S. venustum, or greatly reduced 
and somewhat hook shaped as in S. bracteatum. They sometimes 
bear a spine at the distal end as in S. venustum, a single chitinous 
fingerlike process as in S. bracteatum, or three or four such processes 
as in S. vittatum. The basal pieces (6, b) to which the claspers are 
articulated are divided by a suture near the base. They are very 
large in S. bracteatum and are reduced in S. venustum. The relation 
between the size of the claspers and basal pieces seems to be very 



6 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

constant. If the claspers are large the basal portion is much smaller 
in proportion, and vice versa. 

There are three chitinous plates (a, a, a,) which are situated toward 
the dorsal surface of the hypopygium and surround the anal orifice. 
The two lateral plates are generally armed with spines or stout hairs. 

Ventrad of the plates and extending laterad on each side are two 
narrow chitinous flanges (am,, am) bearing mesally groups of strong 
spines, sometimes in a large number as in S. venustum and some- 
times reduced to only two as in S. hracteatum. These structures 
have been termed by Lundstrom the " arms." Ventrad of these 
spines and not easily distinguishable, extending inwardly, is a long, 
weak, chitinous piece, apparently the sheath of the penis. Ventrad 
and in front of this piece is a triangular troughlike sclerite called 
the adminiculum (ad), which is attached to two strong chitinous 
arms (st, st) , termed by Lundstrom the stylus. 

HABITS OF THE ADULTS. 

COPUEATION. 

The writer has found adults in copula flying near the stream from 
which they were emerging, but they at once separated on being dis- 
turbed. Dr. Sambon informed the writer that in Italy he has found 
the males resting on the reeds in swarms, apparently waiting for the 
females to emerge. 

Dispersion. 

It has been stated by several writers that the females travel long 
distances in search of food, but whether they are prompted by a 
desire for blood or are involuntarily carried away by the wind is a 
matter difficult to determine. 

The writer has been severely bitten by the females of S. johannseni 
Malloch and S. forbesi Malloch in the sand - dune region of 
Havana, 111., at a distance of 5 and even 6 miles from the only pos- 
sible breeding place, which was the Illinois River. The fact that 
the adults crossed a bare and sandy waste with little or no wind, and 
that no males were present, seems to indicate that their flight was 
voluntary. Eiley says that they may be carried 30 or 40 miles. They 
are sometimes attracted to light, as the writer has found a few speci- 
mens flying around a lamp at night. 

Feeding Habits. 

The adult female flies of all the species discussed in this paper, 
with the single exception of S. pictipes, 1 have been frequently ob- 
served feeding on the blood of mammals and, so far as the writer 

1 One female of this species, fully engorged with blood, was taken from a mule's ear by 
Mr. A. H. Jennings at Spartanburg, S. C, in 1912. 



TRANSFORMATIONS OF BUFFALO GNATS. 7 

has observed, are limited to this diet. There are only two definite 
records to the writer's knowledge of Simulium feeding upon any- 
thing other than the blood of mammals. One is by Hagen (1883), 
who states that he found Simulium attacking and feeding upon the 
chrysalids of a butterfly (Pieris) Neophasia menapia Felder. He 
does not, however, state the exact species which he found so doing, 
and remarks that it was similar to the New England "black fly." 
The other record is by H. Pryer, 1 who states that in Japan he found 
Simulium attacking the larva of a sphingid, Smerinthus planus 
Walk., and also the imago of Stauropus persimitis Butl. 

A detailed study was made by the writer in the region of Spartan- 
burg, S. C, of the feeding habits of Simulium venustum, which 
was found from early spring to late fall engorging within the ears of 
horses and mules. Though invariably present on these animals, they 
were seldom found on cattle or on man. The severity of the attacks 
of this species depend both upon the time of year and the time of 
day. It is generally believed that the worst attacks occur in early 
spring and in early fall, and the writer found adults more numerous 
during the first three weeks of September than they had been since 
the middle of June. They appear to be most active from 3 p. m. to 
almost dusk. They are rather easily disturbed while feeding, and 
unless much distended will struggle violently to disengage them- 
selves from the long hairs in the interior of the mules' ears. It has 
been noticed repeatedly that even the well-engorged specimens will 
retract their beaks and successfully fly away and not fall to the 
ground and crawl away to die, as has heretofore been claimed by cer- 
tain writers. The fact that they are so easily disturbed and bite only 
under certain conditions probably accounts for the failure thus far 
of all efforts to get them to engorge while in captivity. While con- 
fined on the human body in a vial they make .frantic efforts to escape 
and after 20 minutes become so exhausted as finally to remain on their 
backs with scarcely a sign of life. Whether the vial was covered to 
exclude the light or not, these experiments were unsuccessful at any 
time of day, both with reared specimens and captured ones. When 
placed in jars containing cloth saturated with defibrinated cow's 
blood a few took a small amount of blood into the crop, but there was 
no distension of the abdomen. 

OVIPOSITION. 

In the method of oviposition the different species of Simulium, 
whose life history has been studied in detail, show characteristic 
adaptations according to their habitat, and may be classified arbi- 
trarily into two distinct groups. Although this grouping applies 
clearly to conditions in South Carolina, it is possible that exceptions 
may be found in other regions. 

1 See Bibliography, p. 35. 



Group 1 contains species normally restricted to rivers which have 
rocky beds and such obstructions as bridge piles, piers, and, in time 
of floods, partly submerged trees. These species deposit their eggs 
at the level of the water, or just below, on any convenient surface, 
such as the bare portions of rocks, sunken posts, and collections of 
water- worn debris, always where the current is exceedingly swift. 
Eggs have never been found by the writer on any surface that was not 
smooth or that was at all covered by moss, algse, or other aquatic 
growths. Of the five species whose methods of oviposition are dis- 
cussed in this article, S. pictipes alone belongs in this group. The 
oviposition and early life history of this species were first described 
by Dr. W. S. Barnard in the American Entomologist in 1880. He 
states that the eggs are long ovoid in form, and gives a figure showing 
them deposited in a vertical position. He also states that the young 
larvae were issuing from the eggs deposited on the rocks above the 
water line and were passing down into the water to begin aquatic life. 
If this was the case, the eggs must have been moistened continually 
by the spray and not left in a dry state, as is implied, the reason for 
which surmise will be discussed at length farther on. 

The eggs of this species which were found by the writer seemed 
to have been deposited indiscriminately in a horizontal as well as in 
a vertical position. The angles appeared rather broadly rounded. 
(PL III, fig. 6.) Surrounded by a viscous substance known as the 
matrix, in which they are fairly evenly distributed, they are laid 
normally in masses on the smooth surface of the rocks just below the 
level of the water. The matrix is brownish yellow at first, after- 
wards turning brown. Usually several females will oviposit in the 
same spot, causing the layers to overlap. 



GBOUP 2. 



Group 2 is made up of species which are peculiar to small streams 
with less force of current and with only submerged herbage or occa- 
sional small collections of sticks and stones to serve as a place for 
the attachment of the immature stages. As a general rule the situ- 
ation selected for oviposition is a grass blade bent at right angles and 
trailing just at the surface of the water and with its surface continu- 
ously moistened. 

/S. mttatum almost invariably oviposits on grass blades in small 
streams. The eggs adhere to the grass blades by a creamy viscous 
matrix entirely covering the eggs. This matrix turns yellowish 
brown on the second day and becomes gradually darker until the eggs 
hatch. The eggs are laid in a single layer, as a rule, very closely 
together. Several females often select the same situation and, as in 
the case of pictipes, the layers often overlap one another. 



TRANSFORMATIONS OF BUFFALO GNATS. 9 

At Dallas, Tex., in March, 1913, JS. vittatum was found by the 
writer ovipositing in considerable numbers on the small stones in 
the limestone bed of a small stream which was almost devoid of 
submerged herbage. The eggs were laid generally below or at the 
surface of the water. In a few instances they were found an inch 
or so above the water, but this was owing to a decrease in the amount 
of water, which varies considerably in this and the majority of 
streams in Texas. This species has been found by the writer on one 
occasion at Havana, 111., ovipositing in large numbers on the bridge 
piles in the Illinois River. The eggs were deposited at or just below 
the level of the water, and as the river was falling at the time at the 
rate of an inch a day, the eggs underwent complete desiccation, and 
all were destroyed. The bridge piles were literally covered with the 
matrix and eggs, and many females, becoming entangled, died adher- 
ing to the viscous masses. This oviposition of this species in the 
main river seems to have been an abnormal occurrence, as the larvae 
have never been found in this situation. Another species, however, 
S. johannseni, according to the writer's observations, breeds: in 
enormous numbers in the main channel in the spring, around the 
submerged vegetation near the banks and wherever there is an 
obstruction. 

S. venustum, in the regions studied, belongs entirely to group 2. 
TKe eggs are laid on submerged grass blades and the like in small 
streams, in situations similar to those selected by S. vittatum. The 
eggs are more evenly arranged than those of that species, the matrix 
is not smeared so profusely, and the egg mass is generally oblong 
in shape and very compact. This species has many times been ob- 
served ovipositing, and specimens which subsequently laid a full 
quota of eggs in captivity were taken from the stream as they 
alighted. 

The oviposition in captivity of S. venustum was observed by the 
writer at Spartanburg, S. C, on September 16, 1913. A female 
8. venustum was noticed at 5.08 p. m. moving up and down a small 
stream within a space of about 4 feet, apparently seeking a suit- 
able place for oviposition. She would touch the water for an in- 
stant and then, apparently dissatisfied, fly up again. This peculiar 
interrupted flight was continued for a period of two minutes, after 
which she alighted on a grass blade which seemed to be satisfactory. 
Immediately a bottle was placed over her and she was at once taken 
to the laboratory. The stream from which the specimen was taken 
was situated 50 yards from the laboratory, and thus little time was 
lost in transit. The bottle in which the specimen was taken was 
partly wet inside. At 5.13 p. m., as soon as the bottle was placed on 
its side, she felt around for two minutes and then settled into posi- 
tion, rapidly thrust out the end of her abdomen, and deposited an 
10981°— Bull. 329—16 2 



10 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

egg about every two seconds, as fast as she could extend and retract 
her ovipositor. Ten eggs were laid in a sort of half circle and then 
the intervening space was filled up until each egg touched another. 
In addition a few were laid a short distance away and the intervening 
space filled up. Oviposition continued steadily until 5.20 p. m., 
when she stopped, turned around, felt the mass with her feet, and 
commenced again. She stopped at 5.21 for 30 seconds and cleaned 
the end of her abdomen. Another lot of eggs was then laid a little 
farther off, in a long, irregular row, about five eggs wide. Oviposi- 
tion was finally ended at 5.27.30 p. m. 

She seemed always to feel for a suitable place before ovipositing. 
A dry spot was invariably rejected. One hundred and forty-five 
eggs were laid from 5.15 to 5.20, about 80 eggs from 5.20 to 5.21 (this 
seemed to be the maximum rate of oviposition), and about 117 from 
5.21 to 5.27.30. The total number of eggs laid was 319. As there 
were two interruptions, one at 5.20 for three seconds and one at 5.21 
for 30 seconds, the length of time spent in oviposition was 12 min- 
utes. The average rate at which the eggs were laid, therefore, was 
about one every two seconds. 

The abdomen was dissected, and only one developed egg was 
found. This was in the oviduct, showing that the oviposition was 
normal, as all developed eggs, with this exception, had been 
deposited. 

S. hracteatum seems to be entirely restricted to the smaller? 
streams, and its method of oviposition is similar to that of S. venus- 
tum in all respects. It is of the same size as venustum and deposits 
about the same number of eggs at one oviposition. 

S. jenningsi is so closely allied to S. venustum that it is extremely 
difficult to distinguish the egg masses of the two species, the main 
points of difference being the smaller size of the S. jenningsi mass 
and the somewhat smaller number of eggs that are deposited. 

The time of day generally chosen for oviposition by these five 
species of Simulium is from about 4.30 p. m. to 5.30 p. m., or even 
until dusk. The weather conditions most favorable seem to be sun- 
shine and lack of wind. Females have been found ovipositing at a 
maximum water temperature of about 95° F. The earliest records 
of oviposition were made by the writer at Dallas, Tex. (latitude 32° 
4' 8"), on March 25, and the latest at Spartanburg, S. C. (latitude 
34° 50"), on November 2. 

There have been various estimates given by authors, both in 
Europe and America, upon the number of eggs laid by Simulium. 
The number of eggs stated to have been laid, or probably laid at one 
oviposition by a single female, varies from 500 to 1,500. This latter 
figure, given for the European species S. reptans L. (S. columba- 






TRANSFORMATIONS OF BUFFALO GNATS. 11 

scheme Fab.), is probably erroneous, as the species is very like S. 
venustum in size and structure. It is the opinion of the writer, 
from many observations, that the largest possible number of eggs 
which are deposited at one time by a single female can not exceed 
500. 

The question whether eggs of Simulium can be subjected to desic- 
cation and then hatch after being immersed again in water is of 
interest, as it has been suggested that in the more or less torrential 
streams found in Texas and the Western States, which flow only a 
few months in the year, the eggs might remain in a dry condition 
during the summer and hatch in the fall or spring with the rising 
of the water. For this reason experiments have been made by the 
writer to ascertain whether Simulium eggs, after partial or complete 
desiccation, would hatch on being again placed in water, as is the 
case with some species of mosquitoes. These experiments all showed 
that at Spartanburg, S. C, the contents of freshly laid eggs became 
completely disintegrated after being thoroughly dried, and that when 
the eggs contained embryos, the latter became distorted on the second 
day after removal from the water, and though they were replaced 
in running water after that period the contents of all finally disinte- 
grated without a single egg hatching. 

When eggs are found at any distance above the water line, the 
writer believes investigation will show that a fall in the water level 
has occurred. The great outbreaks of Simulium in the large rivers 
during the early spring are due primarily to the fact that the rising 
water submerges the growth on the banks and that the water either 
rises or remains at the same level throughout that period, thus pre- 
venting desiccation of the eggs. 

THE EGG STAGE. 

The eggs of Simulium are usually rather triangular in shape, with 
the angles broadly rounded. (PI. Ill, figs. 1-5.) The egg of S. 
pictipes (PI. Ill, fig. 6) , however, is more ovoid in shape than that of 
the four other species dealt with in this paper. The shell, which is 
very tough and apparently somewhat chitinous, withstands the action 
of the water for a considerable period without disintegrating, and 
has been found by the writer in a good state of preservation after 
six weeks in this element. 

The color of the egg when first laid (PL III, fig. 1) is opaque white, 
which changes to yellowish brown as the development of the embryo 
proceeds. The interior of the newly laid egg appears to be an even 
mass of yolk substance. When the egg contains a half -developed 
embryo the yolk substance seems to be consolidated into a central 
mass, indented at both extremities and surrounded by layers of 



12 



BULLETIN 329, IT. S. DEPARTMENT OF AGRICULTURE. 



closely arranged cells (PI. Ill, fig. 2). The interior of an egg con- 
taining an embryo three- fourths developed has a peculiar banded 
appearance (PI. Ill, figs. 3, 4), but as the time of hatching ap- 
proaches the most noticeable features are the cephalic eye spots on 
the embryonic larva, which become more and more distinct. (PL III, 
fig. 5.) Detailed studies on the embryology of Simulium have been 
made by Mecznikow, 1 Kolliker, 1 and Graber. 1 

The average period of incubation, from June to October, of the 
species studied by the writer at Spartanburg, S. C, was about 8.8 
days; the minimum period, 7 days; and the maxium, 12 days. The 
following table will show the normal variation in that region from 
June to October: 

Table shotting period of incubation of eggs of Simulium. a 



T.ot 


Species. 


Date of 
ovipo- 
sition. 


Number of days of incubation. 


No. 


1 


2 


3 


4 


5 


6 


7 


8 


9 


10 


11 


12 


13 


14 






June 12 
June 21 
July 2d 
Sept. 6 
Sept. 11 
Sept. 16 


a 
a 

a 
a 
a 
a 
a 
a 
a 
a 
a 
a 
a 
a 
a 


a 
a 
a 
a 
a 
b 
a 
b 
b 
b 
b 
a 
b 
b 
a 


a 

a 
a 
b 
a 
b 
b 
b 
b 
b 
b 
b 
c 
c 
b 


b 
b 
b 
b 
a 
c 
b 
c 
c 
c 
c 
b 
c 
c 
c 


b 
c 
b 
c 
b 
c 
c 
c 
c 
c 
c 
c 
d 
d 
c 


c 
c 

c 
c 
b 
d 
c 
d 
d 
d 
d 
c 
d 
d 
d 


c 
c 
c 
d 
b 
h 
d 
h 
b. 
h 
b 
d 
b 
b 
d 


d 
d 
c 
b 
c 


d 
h 
d 


b 


b 








2 










3 


do 


b 


b 


b 


b 




4 


S. bracteatum 




T 


do 


c 


c 


d 


b 






fi 






7 


do 


b 














8 


do 


...do 














9 


do 


...do 
















10 


do 


...do 
















11 




...do 
















I 9 


do 

do 

do 

do 


...do 

...do 

...do 

...do 


b 
b 
b 

b 














13 


b 
b 

b 












14 


b 
b 










15 


b 










1 





a Letters indicate stage of incubation, shown on Plate I, as follows: a, corresponds to fig. 1; b, corresponds 
to fig. 2; c, corresponds to figs. 3, 4; d, corresponds to fig. 5; b, date of batcbing. 

The eggs seem to hatch equally well in either still or running water. 
The percentage of eggs that hatch is very high when they are placed 
so that the water reaches them, the average sterility of a series of 
lots kept under observation in normal conditions being from 4 to 5 
per cent. The approximate percentage of egg masses, however, that 
is deposited under such favorable conditions is certainly relatively 
small as compared with the total number deposited, and the location 
of the egg mass seems to be the dominant factor in determining the 
successful hatching of the larva and the consequent abundance of 
the insect. 

THE LARVAL STAGE. 



The larvse of the known species of Simulium, as will be discussed 
at length farther on, are invariably aquatic in their habits and re- 



1 See Bibliography, p. 35, 



Jul. 329, U. S. Dept. of Agriculture. 



Plate III. 







,"■! 



i^kfe 






Eggs and Larva of Simulium. 

Fig. 1.— Egg of Simulium venustum, freshly laid. (After Mecznicow.) Fig. 2.— Egg of Simu- 
lium venustum, second to fourth day. (After Mecznicow.) Fig. 3. — Egg of Simulium venus- 
tum, fourth to sixth day, showing "banded appearance." (After Mecznicow.) Fig. 4. — 
Same, dorsal view. (After Kolliker.) Fig. 5. — Egg of Simulium venustum, just before 
hatching, showing larva in a free condition within the shell. (Original.) Fig. 6. — Egg of 
Simulium pictipes. (Original.) Fig. 7.— Larva of Simulium bracteatum, showing histoblasts 
of pupal filaments, A, A. All greatly enlarged. (Original.) 



Bui. 329, U. S. Dept. of Agriculture. 



Plate IV. 




Heads and Rectal Gills of Simulium Larv/e. 

Fig. 1. — Head of larva of Simulium pictipes. Fig. 2. — Head of larva of Simulium vittatum. 
Fig. 3. — Head of larva of Simulium jcvningsi. Fig. 4. — Head of larva of Simulium venus- 
tum. Fig. 5. — Rectal gills of larva of Simulium jenningsi, typical form. Fig. 6.— Rectal 
gills of larva of Simulium vittatum, variety with small lobes at base. Fig. 7. — Rectal 
gills of larva of Simulium bracteatum, typical form. Fig. 8. — Rectal gills of larva of 
Simulium pictipes, typical form. Fig. 9. — Rectal gills of larva of Simulium venustum, 
typical form. All greatly enlarged. (Original.) 



TRANSFORMATIONS OF BUFFALO GNATS. 



13 





quire swiftly flowing water for their development. The full-grown 

larva of the largest species, according to Johannsen, measures not 

more than 15 mm. in length. The American species 

known to the writer measure from 12 mm. ($. pie- 

tipes) to 3.5 mm. (S. jenningsi). The larvae are 

generally subcylindrical, somewhat attenuated at the 

middle, and with a gradual dilation toward the anal 

extremity. In addition to the head there are 12 

rather indistinct body segments. 

In the larval stage the shape and number of the 
branches of the rectal gills seem to be good sys- 
tematic characters, not differing essentially among 
individuals of the same species. If the number and 

length of the an- 
terinal joints, the 
teeth in the 
mentum, and the 
character of the 
dorsal markings fig. 3.— mmuUum 
of the head are bracteatum. 

, , - t Antenna of 

also USed, the de- larva. Greatly 

termination of enlarged. (Orig- 

, , » inal.) 

half-grown 
larvse is possible. The larvse 
in their last stage can be corre- 
lated positively with their re- 
spective pupae by the dissection and study of the pupal filaments, 
which become fully developed under the larval skin. 

As the larvae of S. bracteatum and JS. jenningsi have not been pre- 
viously described, the follow- 
ing descriptions are given. 

DESCRIPTION OF LARVA OF SIMULIUM 
BRACTEATUM. 

The full-grown larva is from 6 
to 6.5 mm. in length. The general 
color varies from light yellowish- 
brown to grayish, with conspicuous 
brownish markings on the ventral 
surface. The antennae (fig. 3) are 
slender, 4-segmented ; * the second 
segment one and one-half times as 
long as the first; the third segment as long as the first; the fourth a short 
conical process ; the general color pale hyaline ; the first segment infuscate. 

The labial plate (fig. 4) is more strongly serrate than that of 8. venustum 
(fig. 5) : the apical margin rather convex; the middle tooth and each corner 
tooth very large. There are from four to five long bristles near the lateral mar- 
gin on each side. 



M. 



Fig. 4. — Simulium bracteatum. 
larva. Greatly enlarged. 



Labial plate of 
(Original.) 




Fig. 5.- 
lai'i 



-Simulium venustum. Labial plate of 
i. Greatly enlarged. (Original.) 



1 The writer differs from other writers in regard to the segmentation of the antennae. 



14 



BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 



The head (PL III, fig. 7) is light brownish-yellow in color, heavily marked 
with brown on the lateral margins. The dorsal markings of the head are ar- 
ranged in the form of a long central irregular blotch, with 
two adjacent blotches extending diago- 
nally on either side. 

The mandibles are similar to those of 
S. venustum (fig. 12), but darker in color. 
The maxilla? are infuscate and very hairy ; 
the proximal portion of the maxillary 
palpus is dark brown, with a few sparse 
hairs ; the distal end transparent, bearing 
a few conical processes. 

The rectal gills (PI. IV, fig. 7) are 
simple, three branched, somewhat pointed 
toward the distal end, and are curved 
backward cephalically when extended. 
The caudal sucker bears from 60 to 70 
rows of spines or hooks (fig. 6). 

The larvse were taken by the writer from several fig. 7.— SimnUum 
streams in the vicinity of Spartanburg, S. C, from in'tenna^f 
June to October, 1913. They were separated from 
the larvse of other species by the number of the 
branches of the pupal filaments (formed under- 
neath the larval skin) and determined from adults reared from 
them and compared with the tj^pe. 



I 

1 



Fig. 6. — Simulium 

tract eat u m . 
Row of spines 
from caudal 
sucker of larva. 
Greatly en- 
larged. (Orig- 
inal.) 



larva. Greatly 
enlarged. (Orig- 
inal.) 




DESCRIPTION OF THE LAEVA OF SIMULIUM JENNINGSI. 

The larva of Simulium jenningsi is much smaller than 
that of S. venustum and measures from 3.5 to 4.5 mm. in 
length. The general color is light brownish yellow. The 
head is of a uniform yellow with dark-brown blotches of 
characteristic arrangement on its dorsal surface (PI. IV, 
fig. 3), thus differing from venustum (PI. IV, fig. 4), which 
usually has the pigment in these cells lacking. The an- 
tennae (fig. 7) are slender and 4-segmented, the last seg- 
ment being a short conical process ; the first three seg- 
ments are subequal in this 
species, while the antennae 
of venustum (fig. 8) have 
the second segment longer 
than the first. The labial 
plate (fig. 9) is broader 
than that of venustum 
(fig. 5) the teeth more 
even and equal in size, the 
middle tooth not very 
prominent, and there are 
apparently only two large 
and one small bristle along 
each margin, while venustum has four to five large bristles on each side. 
The mandibles are of the usual type, but rather weak and the teeth some- 
what pale. 



t 



Fig. 8. — Simulium 
venustum. An- 
tenna of larva. 
Greatly en- 
larged. (Orig- 
inal. ) 




Fig. 9. — Simulium jenningsi. La- 
bial plate of larva. Greatly en- 
larged. (Original.) 



TBANSFORMATIONS OP BUFFALO GNATS. 



15 







The rectal gills (PI. IV, fig. 5) are three-branched, each lateral branch bear- 
ing six lobes and the middle branch five, as a rule. This is a smaller number 
of lobes than is found in venustum (PI. IV, fig. 9), which 
has seven or eight on each lateral branch. 

The caudal sucker bears from 70 to 75 rows of hooks. 

The larvae were taken by the writer from a fair- 
sized stream near Spartanburg, S. C, in August, 
1913, and were separated from the larvae of other 
species by the number of branches of the pupal 
filaments (formed underneath the larval skin) and 
determined from adults reared from them and com- 
pared with the type. 

EXTERNAL AND INTERNAL STRUCTURES OF THE LARVAE. 

The head is more or less quadrangular in shape 

and very chitinous. The eyes have become reduced 

to mere pigment cells, in the shape of two irregular 

black blotches, situated on each side of the head. 
In addition to the usual mouth parts, the head 

bears a pair of peculiar fan-like organs, situated 

one on each side at the anterior end. The rays or 
cilia of the fans are attached at 
the base each by a strong peduncle 
and range in number from 30 to 
60 according to the species. On 
the inner margin of these cilia are 
fringes of short hairs interspersed with minute 
teeth. As the number of cilia varies in individuals 
of the same species, they are not very reliable 
specific characters. The fans, acting as strainers, 
catch the microorganisms on which the larvae feed 
and sweep them into the mouth. 

The antennae (figs. 3, 7, 8, 10, 11) are situated at 
the sides <©f the head, on the dorsal surface toward 
the cephalic end, just below the base of the fans. 
They are slender, and in the species examined, 
naked. Johannsen says " The antennae are appar- 
ently jointed * * * the first joint twice as 
long as the others taken together; the second, 
slender cylindric * * * the third joint a short 
pointed process at the apex of the second." Miall 
says "Small three- jointed antennae" and gives a 
figure in which the antennae have three long joints 

and lack the short pointed process forming the last joint. Of 

the five species dealt with in this paper, the larvae of Simulium 

venustum (fig. 8), S. pictipes (fig. 10), and S. bracteatum (fig. 3) 




Pig. 10. — Simulium 
pictipes. An- 
tenna of larva. 
Greatly en- 
larged. ( Orig- 
inal.) 



Fig. 11. — Simulium 
vittatum. An- 
tenna of larva. 
Greatly en- 
larged. (Orig- 
inal.) 



16 



BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 



have the antennse 4- jointed, the first long joint described by Johann- 
sen being divided by a very distinct suture. Though the first and 
second joints are very closely articulated and rigid, the constant 
occurrence of a distinct suture between them seems to indicate clearly 
the existence of two segments. The third segment is slender cylin- 
drical, and the fourth a short conical process. 

There are two conical processes situated at the apical end of the 
second segment, which seem to be sense organs. The antennae of S. 
vittatum (fig. 11) are 5-segmented, the second segment being again 
divided. The sense organs are borne on the apical end of the third 

segment. In color the antennae vary with 
the species from yellowish hyaline to dark 
brown. 

The mandibles are situated just below 
the fans and move horizontally. With 
the exception of a slight difference in size, 
according to the species, there are no con- 
stant characters of real systematic value 
in the mandibles. 

The following is a description of the 
mandibles of S. venustum: 

The mandibles (fig. 12) are very chitinous, 
stout, somewhat elongate, with the outer lateral 
margin rounded. There are from two to four 
large teeth at the apex on the inner lateral 
margin, almost dense black in color. Situated 
immediately dorsad along the inner margin of 
the largest tooth is a row of from six to eight 
smaller teeth of the same shape, but much 
lighter in color and gradually decreasing in size. 
Behind this row, on the ventral surface of the mandible, arising generally from 
the third or fourth tooth, is a second row of small, sharp-pointed teeth very pale 
in color, about 10 to 14 in number, which continues along the basal portion of 
the lateral margin of the largest apical tooth. Laterad of this second row of 
teeth, on the inner margin of the mandibles, there is a large wide-angled flat- 
tened tooth, very pale in color, followed by a smaller one of the same descrip- 
tion. Near the apex of the mandible, a short distance from the outer lateral 
margin of the ventral surface, are two large bristles arising from almost the 
same point. At the base of the large apical teeth, on the ventral surface, are 
two clumps of stout hairs. There is a fringe of long hairs on the dorsal sur- 
face of the mandible, which extends halfway down, commencing at the apex, 
where it almost obscures the apical teeth. Opposite the base of this fringe on 
the inner lateral margin of the mandible there is a fan of long hairs, and a 
fringe of very long hairs, which continues down to the base, gradually devel- 
oping into bristles explanate and divided at apex. 

The maxilla? are situated immediately ventrad and mesad of the 
mandibles. The maxillary palpus is short, cylindrical, and bears 
on its distal end several small cone-shaped protuberances similar to 




Fig. 12. — Simulium venustum. 
Left mandible of larva, ven- 
tral view. Greatly enlarged. 
(Original.) 



TRANSFORMATIONS OF BUFFALO GNATS. 



17 




Fig. 13. 



-Simulium vittatum. 
Greatly enlarged. 



Labial plate of larva. 
(Original.) 



those borne on the third segment of the antenna. The lacinia bears 
mesad and cephalad fringes of long hairs and bristles. On its distal 
end there is a single spurlike process. 

The labrum is short, rounded, fringed with long hairs, and is situ- 
ated overhanging the hypopharynx. It is reinforced on its dorsal sur- 
face by a strong T-shaped 
sclerite. The apical mar- 
gin is sometimes serrate. 

The labium (figs. 4, 5, 
9, 13, 14), which almost 
covers the ventral surface 
of the hypopharynx, is 
composed of two or more 
broad chitinous united 
plates. It is immovable. 
The apical edge of the 
ventral plate is serrate. 
The lateral and apical margins of the dorsal plate are also serrate 
and the apical margin usually bears a very prominent central tooth. 
In some species the teeth are trifid, and in others simple. There 
is a row of from three to 10 long bristles near each lateral margin 
of the ventral plate. The number and shape of the teeth and the 
arrangement of the bristles are of systematic value in separating the 
different species, and Robaud and Malloch 1 consider these char- 
acters to be of possible 
generic value. There is 
a certain amount of in- 
dividual variation, but 
seemingly within defi- 
nite limitations. 

The dorsal portion of 
the head in most species 
has distinct markings 
of very characteristic 
arrangement. (PL IV, 
figs. 1-4.) Though sub- 
ject to a certain amount 
of individual variation, they are of systematic value in separating 
the different species especially when combined with other more con- 
stant specific characters. These markings are formed by a collection 
of large cuticular cells which, in some species, such as S. vittatum, are 
strongly pigmented, while in others, such as S. vemistum, they are 
normally almost devoid of pigment, the surrounding area being dark. 




Fig. 



14. — Simulium pictipes. 
Greatly enlarged. 



Labial plate of larva. 
(Original.) 



1 Malloch, J. R. American black flies or buffalo gnats. 
Tech. Ser. no. 26, 71 p. (p. 8), 6 pi., 1914. 

10981°— Bull. 329—16 3 



U. S. Dept. Agr. Bur. Ent. 



18 



BULLETIN 329, U. S. DEPAETMEXT OF AGEICULTUEE. 




i t 9 



Fig. 15. — Sirnulium venustum. Tracheal 
system of larva : dc, dc, dc, Dorsal com- 
missures ; it, initial threads; sp(9), 
spiracular chambers ; hg, hind gut ; rg, 
rectal gills. Greatly enlarged. (Orig- 
inal.) 



The thoracic proleg of Sirnulium 

larvse consists of a single elongated, 
truncate process, attached to the 
second thoracic segment and bear- 
ing concentric rows of minute 
hooks at its apical end, which is 
cup-shaped, and capable of muscu- 
lar contraction, thus forming a 
suckerlike organ, used by the larva 
as means of attaching itself. A 
somewhat similar but very much 
larger suckerlike disk is situated at 
the caudal extremity of the larva. 
The rim is composed of rows of 
strong chitinous hooks as in the 
proleg. The number of rows 
ranges in the different species from 
50 to 110, and the number of hooks 
in a row from 8 to 30. There is 
so much individual variation in the 
number of rows and the number of 
hooks in a row that they are not 
of much systematic value. The 
average number of rows in the 
caudal disks of five species is as 
follows: S. jenningsi, from TO to 
To ; S. venustum, from 55 to 65 ; S. 
bracteatum, from 60 to TO; S. vit- 
tatum, from 65 to 85; S. pictipes. 
from 130 to 110. S. pictipes has 
by far the greatest number of rows, 
very close together and from 25 to 
30 hooks in each row. It is the 
only one of these five species that 
can be positively determined on 
these characters alone. 

RESPIRATORY SYSTEM OF THE LARVAE. 

The tracheal system of the larva 
(fig. 15) consists of two main lon- 
gitudinal trunks, connected by 
commissures, which lead to the 
spiracular chamber. Extending 
from the spiracular chambers are 
thin chitinous rods (the initial 
threads), which lead to the oval 



TRANSFORMATIONS OF BUFFALO GNATS. 19 

thickenings of the cuticle known as the spiracles. The spiracles do 
not seem to be functional as a means of respiration. 

Respiration apparently takes place by what are known as the 
rectal gills (PL I, fig. 2, rg), which are extensions of the rectal wall 
and are formed of the same epithelial layer. These extensions are 
primarily 3-branched, and are either simple or bear numerous lobes. 
Minute tracheolae penetrate these gills, joining the main trunks at the 
base of the rectum. The gills are also filled with blood, are retractile 
into the rectum, but are usually extended in running water. Accord- 
ing to Headlee, they function both as blood gills and as tracheal gills, 
as the presence of blood in them is undoubted, and since the tracheae 
in them are very minute. The tracheal system can be seen very dis- 
tinctly in living larvae. Several larvae, still quite active, were placed 
in a shallow dish of water and examined under the binocular by the 
aid of strong sunlight against a black background. As the larvae 
slowly died the tracheae, owing to the air collected in them, showed 
a bright silvery appearance, so that even the very small ramifications 
and branches could be clearly distinguished. The larvae seem to be 
in a comatose condition an hour or so before death, and the silvery 
appearance of the tracheae remains for about three hours after death, 
so that there is a considerable period in which the tracheae may be 
studied before the air is driven out. In larvae preserved in alcohol or 
mounted in balsam the air, of course, is driven out of the tracheae, 
which becomes almost transparent, so that it is very difficult to trace 
them in this condition. The tracheae become greatly ramified toward 
the caudal end of the body and seem to penetrate the wall of the 
alimentary tract and to extend into the rectal gills. 

Larvae have not been found to survive longer than forty-eight 
hours in still water, and on being transferred from flowing water will 
turn back constantly in an effort to clean the rectal gills with the 
mouth parts. Larvae placed in still water and only barely covered 
will survive longer than those covered to a depth of 3 inches or more. 
That the lack of oxygen is responsible for the death of the larvae 
transferred from flowing to still water is further evidenced by the 
fact that the larvae will survive longer in a tightly corked bottle at 
a temperature of 32° F. than at a temperature of 75° F., because the 
amount of oxygen that can be held in solution by the water varies 
inversely as the temperature. Larvae seem to thrive equally well in 
running water, whether the temperature is 32° or 75° F. Low tem- 
perature seems to retard but not to injure development, and a rising 
temperature up to 75° F. hastens development. 

The structure of the rectal gills and the number of lobes afford 
excellent systematic and specific characters, as may be seen from 
the accompanying figures (PI. IV, figs. 5-9). The variation in indi- 
viduals seems to be bounded by well-defined limitations. 



20 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

LARVAL DEVELOPMENT. 

From 12 to 16 hours before hatching the young larvae are in an ap- 
parently free condition within the shell. There is an almost con- 
tinual movement of the head, which is forced against the ectoderm 
by sudden convulsive movements of the body. The shell suddenly 
splits and the larva at once emerges, literally tumbling out. The 
split reaches from the cephalic end of the egg to the middle, generally 
a little to the left. It is evident from the clear appearance of the 
alimentary tract of the newly emerged larva that the ectoderm is 
not eaten away at all. The larva at once clings to the nearest point 
of attachment by its thoracic proleg and waves its anal portion 
around several times, evidently to clear the rectal gills. It then 
attaches itself to the nearest object by the peculiar suckerlike organ 
on its anal extremity and thrusts out its gills at intervals of about 
15 seconds. It at once commences to feed on the matrix surround- 
ing the eggs and the adjacent microorganisms, using its thoracic 
proleg as a scoop, with a constant movement of this organ toward the 
mouth parts. In still water the fans are not used for sweeping in 
the food for some hours after the larvae have hatched, but remain 
appressed to the sides of the head. 

The newly hatched larvae of all the species described in this paper 
measure from two-thirds to three-fourths of a millimeter in length. 
The structure of the larvae in the first instar, of the species examined 
by the writer, is fundamentally the same as in the last, with the 
exception that the head is larger in proportion to the rest of the body 
and the general appearance very transparent, due to the lack of pig- 
mentation and the empty condition of the alimentary tract. The 
black eye spots on the sides of the head are very prominent, and the 
dorsal markings of the head, though not so distinct as in later stages, 
are easily distinguishable. The silk glands are employed almost at 
once after hatching to form a silken thread, which is used to hold the 
larva in position in the current. The structure of the rectal gills 
seems to remain the same throughout larval development. 

LARVAL HABITS. 

MOLTING OF THE LARVAE. 

According to Strickland 1 the larvae do not shed the entire skins 
but only the skeleton of the head. The writer has found that the 
entire skin is shed, as larvae have been found which had partly cast 
off the entire skins, bearing the chitinous hooks of the caudal sucker, 
and which showed the caudal sucker again developed in the new 
larval skin. The entire skeleton of the head is cast off toward the 

1 Strickland, E. H. Some parasites of Simulium larvae and their effects on the develop- 
ment of the host. (In Biol. Bui., v. 21, no. 5, p. 302-338 (p. 303), 5 pi., Boston, 1911. 



TRANSFORMATIONS OF BUFFALO GNATS. 21 

front at molting, and the remainder of the skin toward the caudal 
extremity, the tracheae being withdrawn through the spiracular open- 
ings. The number of molts has not been determined. 

MIGRATORY HABITS AND LOCOMOTION OF THE LARVAE. 

On being suddenly disturbed or on the diminishing of the current, 
the larvae let themselves be carried down stream steadied by the silken 
thread previously described, which they have attached to some sta- 
tionary object, and seek a more favorable situation. In many in- 
stances the larvae have been observed almost to regain their former 
position, by winding up the thread with the thoracic proleg and 
mouth parts, but as a rule they are unable to work against the current. 
The method of locomotion in still water is similar to that of geo- 
metrid larvae. By looping the body, they bring the anal extremity 
forward beside the proleg, which is then released on the caudal sucker 
again obtaining a firm hold. 

A heavy rain causing a sudden swiftening of the current will 
often entirely change the distribution of the larvae. This fact is of 
considerable economic importance, as it may account for the sudden 
appearance of Simulium in localities usually exempt. This was well 
illustrated in the following instance, observed by the writer at Spar- 
tanburg, S. C, A fair-sized stream had been free from larvae for 
two months or more, when one of the tributaries near its source be- 
came heavily infested with young and half -grown larvae. A heavy 
rain and consequent washout carried practically every larva from 
the tributary down the large stream for nearly a mile, where they be- 
came successfully established, causing a subsequent heavy infestation. 

Young larvae seem to migrate more readily than full-grown larvae. 
Several experiments were tried in regard to this. A vessel containing 
larvae of "all sizes was placed under a running faucet, causing the 
vessel to overflow. The full-grown larvae as a rule remained in the 
comparatively still water within the vessel, often spinning their 
cocoons and successfully pupating. The young and half-grown 
larvae seemed invariably to detach themselves and would be found 
within two hours gathered on the surface over which the water was 
flowing. 

At one time the attention of fish culturists was drawn to Simulium, 
as the larvae were stated to cause the death of young trout by en- 
tangling them in a silken web. This was disproved in the American 
Entomologist and Botanist, in 1870, by Mrs. Sarah J. McBride, 1 who 
clearly demonstrated that the "death web of young trout" was a 
myth, and that the threads were not strong enough, or interwoven, 
so that fish could be entangled in them. 

1 See Bibliography, p. 35. 



22 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 



THE FOOD OF THE LARVAE. 



The food of the larvae is entirely microscopic. There are various 
accounts given on this subject by different authors, and they are 
somewhat divergent. Riley says that they feed on animalcules, but 
do not disregard microscopic matter of vegetable origin. He also 
states that larvae kept in a jar were seen to swallow the minute larval 
forms of small crustaceans belonging to the Copepoda and Isopoda, 
and that a number of square diatoms, joined together in chains, were 
found in the alimentary tract. 

Miall says that he has found in the alimentary tract flinty valves 
of diatoms, desmids, and pieces of small crustaceans. 

Kellogg, in his article on the food of Simulium and Blepharocera, 
states that he found thousands of tiny siliceous shells of diatoms in 
the intestines. They caused considerable difficulty in the making of 
microscopical sections for histological study. He also states that the 
larvae feed on the stalked Gomphonema and occasionally on the 
genus Nitzschia. They are also stated to feed on Vaucheria and 
Nothrix. 

The writer has found that the color of the larva varies according 
to the nature of the stream, and that the larvae seem to thrive best 
in streams containing the largest proportion of such organisms as 
Euglena viridis and Spirogyra. Larvae in running water were ob- 
served feeding in specially constructed glass tanks, and were seen 
to reject large Paramoecia and apparently anything except the 
smallest particles of the plankton. A striking fact seemed to be 
the effect of different foods upon the color of the larvae. When the 
tank containing the food of the larvae was filled only with water, 
decaying vegetable matter, and living grasses, the larvae became 
emaciated and starved to death; but on the introduction of green 
algae and Spirogyra, they regained their vitality and the alimentary 
tract changed from a light brownish yellow to a bright green. Dis- 
sections of the alimentary tract showed normally a quantity of green 
rod-like algae, flinty shells of diatoms, and some minute star-shaped 
animalculae. The larva of Simulium pictipes, which lives in the 
larger streams, has the alimentary canal filled with a quantity of 
sand; and the color is always brown corresponding to the brown 
growths on the rocks. The streams in South Carolina, which were 
contaminated by chemical refuse from the cotton mills, were abso- 
lutely free from larvae, and this fact is of economic importance as it 
may be utilized further in the control of the larvae. Pure animal 
sewage is not deleterious to the growth of the larvae, provided the 
other environmental factors are favorable. 



TRANSFORMATIONS OF BUFFALO GNATS. 23 

THE PUPAL STAGE. 

METHODS OF PUPATION. 

The histoblasts of the pupal and adult organs are formed in 
Simulium larvae some considerable time before pupation takes place, 
and can be discerned when the larvae are half grown, shortly after 
the second molt. The pupal respiratory organs, composed of long 
tubelike filaments (PL V, fig. 1), can be seen underneath the larval 
skin, on the sides of the anterior portion of the thorax, lying coiled 
up and visible as rounded darkened areas which become almost black 
as the pupal stage approaches. (PL III, fig. 7, A, A.) Shortly after 
the molt preceding pupation the chitinous hooks on the dorsal and 
ventral surfaces of the abdomen of the pupa become well developed 
underneath the larval skin. 

Before commencing to pupate the larva spins over itself a pocket- 
shaped pupal case, formed of the strong silken threads supplied by 
the salivary glands. The shape and texture of the pupal cases vary 
according to the species. Of the five species discussed in this paper, 
four have pupal cases of the shape that may be described as the 
u wall-pocket " type, the texture finely spun, almost leathery in ap- 
pearance, the cases being spun as a rule well separated from one 
another, and the distal end wide and rather open. (PL V, fig. 2.) 
S. pictipes is the exception, having the pupal case shaped after the 
fashion of a boot (PL V, fig. 5), the heel always pointing down- 
stream, the pupal cases often overlapping one another in a coral- 
like formation, the texture coarsely spun, very tough, and the distal 
end narrow. 

Shortly before the larva has finished making the pupal case the 
air from the tracheae, entering the extension leading from the base 
of the main trunk from which the branch filaments arise, slowly 
creeps along the entire length of the filaments. The skin splits along 
the dorsum of the thorax and the filaments are at once projected 
into the water. The skin behind the head is then worked off toward 
the caudal end of the larva and the old tracheae are withdrawn 
through the spiracular openings. The inner lining of the hind gut, 
together with the anal gills, which are formed of the same epithelial 
layer, is then cast out through the anal slit which is situated just 
above the X-shaped sclerites on the dorsal surface at the posterior 
end of the larva, and may be seen attached in the interior of the 
cast larval skin, which often remains for a while within the pupal 
case. The skeleton of the head of the larva is then pushed off down- 
ward to the front, the wall of the alimentary canal, about as far as 
the junction of the pharynx and the oesophagus, coming away with it. 
The pupa seems to lock itself in the pupal case by means of the 



24 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

strong hooks on the dorsal and ventral surfaces of the abdomen. 
These hooks are turned anteriorly on the dorsal surface on segments 
2, 3, and 4 ; posteriorly on the dorsal surface of segments 7, 8, and 9, 
and all hooks on the ventral surface are turned anteriorly. The 
whole operation of pupation and of spinning the pupal case takes 
from 45 minutes to 1 hour. 

GENERAL DESCRIPTION. 

The pupae of Simulium at first are generally golden yellow or light 
brown, the color and shape of the adult organs showing very clearly 
through the pupal skin as the time of emergence approaches. There 
are nine abdominal segments. On each side of the thorax are situ- 
ated the respiratory organs, composed of long chitinous tubes, aris- 
ing from a main stalk, tapering somewhat, and usually branching 
dichotomously toward the distal end. The number of filaments, 
always, counting the branches of the distal ends, varies according to 
the species, from 4 to 60, and is an excellent systematic character, 
as it is very constant for each species. On the dorsal and ventral 
surfaces of the abdomen are situated rows of strong chitinous hooks. 
These seem to be of little use as distinguishing characters for the 
five species discussed in this paper, as they are approximately the 
same in number and have about the same position in each. The 
pupae can be positively correlated with the adults by the dissection of 
mature male pupae and study of the genitalia. 

The pupae of S. hracteatum and S. jenningsi have not been pre- 
viously described, and the following descriptions are given: 

DESCKIPTION OF PUPA OF SIMULIUM JENNINGSI. 

The pupa of 8. jenningsi (PI. V, fig. 4) is not more than 2.5 mm. in length, 
and is golden yellow when first formed. 

The respiratory filaments, which are situated at each side of the thorax near 
the head, are each composed of a single main trunk, which divides at base into 
the following branches : Four single unbranched filaments and two long fila- 
ments, each of which divides again dichotomously, making eight branches in 
all, counting the distal ends of the branches. 

On the dorsal surface of the abdomen there is a row of very small hooks on 
each side of the second segment, and on the third and fourth segments rows of 
four very large hooks on each side pointing cephalad. On the fifth segment 
there is a row of hooks pointing caudad, and on the ninth segment a row of 
minute hooks near the cephalic margin and a single large hook on each side 
at the middle of the segment. On the ventral surface of the abdomen there 
are two large hooks close together on the fifth segment, and two large hooks, 
rather far apart, on each of the sixth and seventh segments. The caudal end 
of the pupa is cleft for a short distance in the middle. 

The pupae studied were reared from larvae and determined from 
adults reared from them and compared with the type. 



Bui. 329, U. S. Dept. of Agriculture. 



Plate V. 




PUP/E OF SlMULIUM. 

Fig. 1.— Respiratory filaments of pupa of Simulium vittatum. Fig. 2.— Pupa of 
Simulium venustum, in pupal case. Fig. 3.— Pupa of Simulium bracteatum: A, 
side view of filaments. Fig. 4.— Pupa of Simulium jenninc/n. Fig. 5.— Pupa of 
Simulium pictipes, in pupal case. All greatly enlarged. (Original.) 



TRANSFORMATIONS OF BUFFALO GNATS. 25 

DESCRIPTION OF PUPA OF SIMULIUM BEACTEATUM. 

The pupa of 8. bracteatum (PI. IV, fig. 3) measures about 4 mm. in length and 
is of a golden yellow color when first formed. 

The respiratory filaments are composed of a single main trunk on either 
side of the thorax, each of which divides in the following manner: Two long 
branches arise from the base of the main trunk, which again divides a short dis- 
tance farther up, making four long branches on each side, counting the 
branches at the distal ends. The hooks on the abdomen are arranged as usual. 

The pupae were reared from larvae and determined from adults 
reared from them and compared with the type. 

DURATION OF PUPAL STAGE. 

The duration of the pupal stage of S. venustum, according to 
Mrs. Sarah J. McBride, at Mumford, N. Y., is three weeks. The 
maximum period in the pupal stage of the same species observed by 
the writer was nine days at Havana, 111., late in the fall, the average 
temperature during that period being 36° F. 

The minimum period in the pupal stage of S. venustum was a little 
over 84 hours at Spartanburg, S. C, during the month of June, with 
a temperature from 70° to 90° F. The average length of the pupal 
period for the five species under consideration, during the summer, 
is from five to seven days. 

The general effect of low temperature seems to be to retard, and 
of rising temperature up to 90° F. to hasten the emergence of the 
adult from the pupa. The effect that low air temperature has on the 
pupa in retarding development is much less in proportion than the 
effect that a rising temperature between 60° and 80° F. has in 
hastening emergence. Though their structure is normally adapted 
for aquatic life, yet when they are exposed to the air, as sometimes 
happens when the water falls, they will often emerge even after 24 
hours spent out of water if the adult is sufficiently developed within 
the pupal skin. This was especially noticeable at Havana, 111., in 
1912, when the river began to fall. 

The respiratory system of the pupa is a modification of the general 
tracheal system of the larva. The rectal gills having been cast off, their 
function appears to be assumed by the tubelike filaments arising on each 
side of the thorax. There are two long main trunks extending down 
each side of the abdomen. These give off branch tracheae, connected 
by commissures, which lead to the abdominal spiracular chambers, 
from which arise the initial threads leading to the spiracles. The 
spiracles are cuticular invaginations and become closed, according to 
Taylor, 1 on the withdrawal of the old tracheae at the time of the 

1 Taylor, T. H. On the tracheal system of Simulium. In Trans. Ent. Soc. London, 1 
1902, p. 701-716 (p. 703), 8 fig., 1902. 



26 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

shedding of the larval skin. From the mesothoracic spiracular cham- 
ber extends a broad tracheal trunk leading to the base of the main 
trunk of the respiratory filaments, which do not contain tracheae, but 
are hollow. According to Taylor, 1 the air is not taken directly into 
the gill base from this hollow space, but is absorbed through the 
external chitinous fibrillae and thence into the tracheal extension 
through a membrane. 

EMERGENCE FROM THE PUPAL STAGE. 

Four or five hours before emergence there is a very noticeable in- 
termittent movement of the adult within the pupal skin, which is 
gradually distended with air toward the anal extremity, the abdomi- 
nal tracheae being probably withdrawn through the spiracular open- 
ings. Coincident with this the anal portion of the adult is with- 
drawn from the pupal skin and a threadlike membrane, seemingly 
the lining of the hind intestine, may often be seen extending from 
the anus of the adult to the pupal skin, to which it remains attached 
after emergence. As the pupal skin is locked by the strong chitinous 
hooks to the pupal case, the adult exerts a strong pressure toward the 
cephalic end and the pupal skin splits along the dorsal portion of the 
thorax and head, forming a T-shaped aperture. The adult at once 
rises to the surface of the water surrounded by a bubble of air which 
has been collected in the distended pupal skin, and running along the 
surface of the water at once takes flight. The curious way in which 
the adult rises to the surface surrounded by a bubble was commented 
on by the earliest writers on the group, and in situations where the 
pupae are found in thousands, as in parts of Hungary, and along the 
Illinois and Mississippi Rivers in America, the water seems almost to 
boil as they emerge. 

LIFE CYCLE AND NUMBER OF GENERATIONS. 

The number of generations varies according to the species and 
the latitude. In the Southern States the species seem to breed con- 
tinuously from about the middle of March until the approach of 
severe cold weather, generally about the end of November. The life 
cycle of one generation during the summer takes approximately four 
weeks ; 7 days in the egg stage, 17 days as larvae, and 4 days as pupae. 
The time from the egg to the adult stage varies according to the rise 
and fall of the temperature. There are probably from five to six 
generations annually in South Carolina of the species here dealt 
with, except S. pictipes. which normally has three generations. In 
Illinois there are only three or four generations of S. venustum 
annually. 

1 Loc. cit. 



TRANSFORMATIONS OF BUFFALO GNATS. 27 

INSECT ENEMIES AND PARASITES. 

The larvae of Simulium are often parasitized by nematode worms 
of the genus Mermis, specimens of which have been found by the 
writer measuring 12 mm. in length. These were found in larvae of 
JS. venustum, coiled around the intestines, and extended from near the 
caudal end to the thorax. The specimens that attained the greatest 
length were found singly, but as many as four have been found in 
individual larvae. According to Strickland (1911), 1 the Mermis 
retard the development of the pupal and adult histoblasts, cause 
the death of the larvae, and escape through punctures made in the 
epidermis. He also states that in the vicinity of Boston, Mass., 
Mermis was found parasitizing larvae only during the spring, and 
that there is a seasonal variation of parasitism. The writer, while in 
South Carolina, found species of Mermis parasitizing larvae from 
May until late in October, and these larvae seemed to have developed 
the pupal histoblasts to a much greater extent than is estimated by 
Strickland. The larvae are also heavily attacked by glugeid and 
gregarine species of Myxosporidia. 

The writer has found the larvae being attacked by species of 
Hydropsyche in Illinois and South Carolina. Dr. Howard (1888) * 
also mentions this fact in his article on a species of Simulium at 
Ithaca, N. Y., and gives a fuller account in the Annual Report of the 
U. S. Commissioner of Agriculture for 1886, page 510. Species of 
minnows attack the larvae frequently, and Eiley 2 mentions that the 
small fishes of the family Cyprinidae also feed on them. 

The pupae, so far as is known, are not parasitized by Mermis or 
Myxosporidia. The adults have been found by the writer at Spar- 
tanburg, S. C, to be frequently parasitized by nematode worms of 
the genus Mermis, which were usually found singly. In one in- 
stance three of the worms were found in a female S. venustum. 
The same number were found in a female of S. bracteatum. They 
were situated in the abdomen, coiled around the Malpighian tubes 
and intestines, and in some cases extended into the thoracic region. 
The vitality of these specimens infested by the Mermis seemed to be 
seriously affected, though they lived for some time, 31 hours being 
the minimum and 72 the maximum period. All of these specimens 
thus parasitized were reared from pupae, with the exception of one 
adult female of S. hracteatum, which was taken flying around a lamp 
at night. No adults taken biting on animals were ever found to 
contain Mermis. 

1 See Bibliography, p. 35. 

2 Riley, C. V. Report of the Entomologist. In Rept. U. S. Comr. Agr. f. 1886, p. 459- 
592 (p. 510), 11 pi., 1886. 



28 

Georgewitch x describes a trypanosome, Crithidia simuliae, which 
he found in the stomachs of adult females taken biting cattle, etc. 
The locality in which the animals were attacked was a district in 
Servia, and the species S. reptans (=S. columbaschense) . He did 
not. however, find any similar organism in the blood of the animals 
attacked. 

Riley 2 states that Lugger observed them being attacked by Asi- 
lida? and Odonata. 

TTise (1911) 3 reports that in British Guiana the adult females of 
Simulium are attacked by a voracious enemy in the nature of a black 
and white wasp (probably Monedida signata), which follows the 
aboriginal Indian to obtain the " Pium " (Simulium). This wasp 
reduces the " Pium " to unconsciousness, deposits eggs, and leaves the 
body to be fed upon by the resulting larvae. 

SIMULIUM AS A POSSIBLE CARRIER OF DISEASE. 

In 1874 J. P. Megnin 4 strongly advanced a theory that two species 
of Simulium in the Department of the Ehone, France, are the trans- 
mitting agents of virulent charbon. He also mentions Stomoxys 
and Haematobia in this connection, but places most emphasis on 
Simulium, whose habits more closely conform to the outbreaks and 
distribution of the disease in that locality. He also states that, 
in his opinion, M. Tisserant, sent by the French Government to 
investigate the subject, proved that Simulium was the cause or 
the transmitting agent of the disease. In a later paper he reaffirms 
his statements and mentions that he has found a "Psoriasis 
guttata " prevalent in the ears of horses, and believes it is due 
to the bites of Simulium. The writer has found a similar condition 
to be very common in the ears of horses, undoubtedly due to the bites 
of Simulium. in Illinois, South Carolina, and the vicinity of Wash- 
ington, D. C. As this condition may be of a purely secondary nature, 
and as apparently no experimental or careful analytical work has 
been done on the subject, all statements regarding the transmission 
of a disease of cattle by Simulium must be regarded as purely theo- 
retical. 

According to Eiley and other authors, S. pecuarum Eiley and S. 
jneridionole Eiley were supposed to carry cholera among chickens 
and hogs, but nothing definite was ascertained on this point. 

1 Georgewitch, Jivoin. Sur un Trypanosomide nouvean, Crithidia simuliae, n. pp. d'une 
Simulie (Simulium columbacensis) de la Serbie septentrionale. In Compt. Rend. Soc. 
Biol., t. 67, no. 31, p. 480-482, 1 fig., Nov. 12, 1909. 

2 Op. cit., p. 510. 

3 See Bibliography, p. 35. 

4 Du role des moucbes dans la propagation du charbon et autres affections virulentes. 
In Jour. Med. Veter. Mil., t. 12, no. 8, p. 461-475, Paris, Jan., 1875. 



TRANSFORMATIONS OF BUFFALO GNATS. 29 

In 1905 Dr. Louis Sambon advanced the theory that pellagra might 
be transmitted by a blood-sucking fly of the genus Simulium. An 
accurate knowledge of the biology of the genus is very necessary in 
order to prove or disprove such a theory. It must be proved that 
Simulium not only bites in very large numbers, in order that a suffi- 
cient percentage of specimens will become infected which will live 
and become capable of transmitting pellagra, but it must also be 
proved that they will bite man after they have become infected, 
since hereditary transmission is probably entirely out of the question. 
Simulium exists in many places in large numbers, and if it should be 
proved that it normally requires a meal of the blood of vertebrates 
before it can fully develop the ovaries, then the chances that it may 
become infective are greatly increased. 

Evidence on these points may be obtained in the following three 
ways: 

(1) By rearing adult females from the immature stages, and then 
allowing them to engorge, oviposit, and reengorge. This method 
was tried a number of times, but with no success, for the fly will not 
readily engorge while in captivity, as was noted in the discussion of 
the feeding habits of the adult. 

(2) By the capture of adults actually feeding on mammals, and by 
inducing them to oviposit and then to reengorge. This method also 
was unsuccessful for the same reasons. 

(3) By dissections. If it could be proved that when a Simulium, 
which has once engorged on blood and oviposited, is still in a condi- 
tion favorable to a second oviposition — that is, if rudimentary eggs 
are present in the ovaries awaiting only a second blood meal for their 
successful development — then there would be a more definite basis 
for a theory of disease transmission as opposed to the theory of merely 
a close coincidence in the distribution of pellagra and Simulium. 
This is the method adopted by the writer and is the one discussed in 
the following pages. The experiments were concluded in Spartan- 
burg County, S. C, a country very favorable for the production of 
Simulium, being hilly and with a network of small streams, rapid 
and especially suitable for the development of the immature stages. 
The experiments on the actual biting and feeding habits were carried 
on more or less continuously from June 13 to September 16. The ma- 
terial for these experiments consisted of specimens of 8. venustum; 
a good series of reared specimens (about 30) ; a number of females 
found engaged in oviposition; about 300 females all of which were 
taken in the act of engorging on mammals. Of the last named only 
about 90 were successfully dissected, as the engorged adults after 
death became internally disintegrated and hardened after an hour 
or so, despite every precaution. Many also died between midnight 
and 7 a. m., or while they were being transported from the place of 



30 

capture to the laboratory. The adults, with the exception of 10 speci- 
mens killed at the time of capture, were kept alive as long as possible 
and dissected as soon as death was imminent. Some, in order that 
data might be obtained on their condition at the time of engorge- 
ment, were killed when captured and dissected within an hour. 

RECORDS OF DISSECTIONS. 

DEVELOPMENT OF THE OVARIES OF EEAEED NONFED ADULTS. 

In order to have a check on the experiments with engorged adults, 
32 females reared from isolated pupse were kept alive as long as possi- 
ble, without food, in bottles containing damp cloths. There were a 
number of males, reared from this same lot of pupse, at liberty within 
the breeding cage together with these females, and copulation prob- 
ably took place, but no definite statement can be made with regard to 
this point. Four females were killed and dissected within 6 hours 
after emergence. The remainder lived from a minimum period of 
14r| hours to a maximum of 119 hours. All these specimens on dissec- 
tion contained rather transparent ovaries of great potential develop- 
ment and full of round eggs (stage 1) (PL I, fig. 1, p. 4). In no 
instance did any one of these specimens develop the eggs within the 
ovaries as far as even the second stage. The maximum longevity of 
any nonfed reared specimen exceeded the maximum longevity of any 
specimen taken after engorgement by 52 hours. It would seem, 
therefore, that of these 32 reared specimens, there would have been 
1 or 2 which would have developed the eggs within the ovaries, if it 
had been in the natural course of events for them to do so. 

CONDITION OF THE OVAEIES OF FEMALES FOUND OVIPOSITING. 

Eleven females were taken actually engaged in oviposition on grass 
blades in streams. When these specimens were dissected, there was 
found in each stomach a certain amount of substance closely resem- 
bling the digested blood found in engorged specimens which had 
lived after engorgement for 40 hours or more previous to their dis- 
section. A chemical test for haematin was applied to the substance 
found in the stomachs of the females found ovipositing, in order to 
prove beyond doubt whether it contained animal blood or not, but, 
owing to the small quantity and the changes consequent to the process 
of digestion, it was impossible definitely to determine its character. 

Three specimens were taken from grass blades in a stream on which 
they had just alighted and had not begun to oviposit. These speci- 
mens were at once dissected, and their ovaries were found to contain 
from 250 to 300 fully developed eggs. Four specimens were taken 
from egg masses deposited in the same situation, which had evidently 



TRANSFORMATIONS OF BUFFALO GNATS. 31 

just finished ovipositing. Four others which subsequently laid from 
89 to 349 eggs while in captivity were also captured. The adults 
lived after oviposition from 15 minutes to 67 J hours, and were dis- 
sected immediately after death. Their ovaries were found to contain 
in each case a large quantity of eggs of the round type corresponding 
to stage 1 (PL I, fig. 1) with the exception of the specimen which 
lived only 15 minutes after oviposition and in which the eggs within 
the ovaries were only visible under a high magnification. The ovary 
of one specimen contained in addition, near the oviduct, a large fully 
developed egg which had not been deposited. This last-mentioned 
condition (stage 5, PI. 1, fig. 5) was also found in adults taken 
engorging upon mammals and killed at the time of capture. 

CONDITION OF THE OVARIES OF ADULTS TAKEN FEEDING ON MAMMALS. 

In order to demonstrate the relation between the amount of en- 
gorgement and its apparent effect upon the development of the eggs 
within the ovaries, the condition of the ovaries is discussed collect- 
ively with regard to the previous amount of engorgement by adults, 
irrespective of the dates on which the adults were captured. 

The following symbols are used in description to separate the 
varying degree: ( + ) Slight and partial engorgement, or about one- 
fourth the utmost capacity; (-| — \-) fair engorgement, or one-half the 
utmost capacity; (-j — | — |-)well engorged, or three-fourths the utmost 
capacity; (-| — 1 — | — \-) complete engorgement, or distension of the ab- 
domen to its utmost capacity. 

CONDITION OF THE OVARIES OF ADULTS KILLED AT TIME OF CAPTURE. 

Ten adults were taken from time to time engorging on the blood 
of mules. They were killed at once to obtain data on the condition 
of the ovaries at the time of engorgement. Two specimens were 
slightly engorged ( + ) ; in one the ovaries showed a condition corre- 
sponding to stage 5, each ovary containing about 12 fully developed 
eggs, the remainder of the ovary being filled with eggs of the round 
type ; in the other the ovaries contained only eggs of the round type 
in large quantity (stage 1). One specimen was half engorged 
(-) — |-) ; its ovaries were in a condition typical of stage 5, being filled 
with small round eggs and containing in addition 8 large fully de- 
veloped eggs in a free condition, which seem positively to have been 
developed at a different period from the rest of the ovaries. One 
specimen was fairly engorged (-] — | — \-) ; the ovaries contained only 
eggs of the first stage in large numbers (stage 1). Six specimens 
were taken fully engorged (++++); all of the ovaries were in a 
condition typical of stage 1, the eggs being of the small round type, 
translucent, and in large numbers. 



32 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

In conclusion, there were only two stages found in the ovaries of 
adults killed at the time of capture, either small, round, undeveloped 
eggs in large quantity (stage 1), or round undeveloped eggs with 
the addition of a very few large, fully developed eggs (stage 5). 
This latter stage is presumably the result of a previous engorgement 
and oviposition. 

CONDITION OF THE OVARIES OF NONENGORGED ADULTS TAKEN ON ANIMALS. 

Six specimens, which had evidently just alighted and had not fed 
on that particular animal, were taken at various times from mules' 
ears. They lived from 2 to 47 hours after capture, and the condition 
of the ovaries in all these specimens was typical of stage 1. There 
was no development of the eggs within the ovaries, and the condition 
seemed to be the same as in adults reared from pupee and dissected 
shortly after emergence. 

CONDITION OF THE OVARIES OF PARTLY ENGORGED ADULTS. 

Twelve specimens were taken which had partly engorged (+). 
The eggs within the ovaries of five of these specimens were not de- 
veloped at all, and showed a condition corresponding to stage 1. 
These lived from 16 to 30 hours after capture. Three specimens 
showed the ovaries in a condition typical of stage 5, with from 1 
to 4 fully developed eggs near the oviduct, and with the remainder 
of the ovaries filled with the small round type. These individuals 
lived from 12 to 21 hours after capture. The ovaries of two speci- 
mens which lived for 52 and 53 hours, respectively, contained a large 
number of eggs between stages 2 (PL I, fig. 2) and 3 (PL I, fig. 3), 
almost oval in shape, about 200 in all. Two adults were slightly 
more engorged than the rest, though not quite half engorged. They 
contained ovaries with eggs fully developed, of the same size and 
shape as eggs freshly deposited, but in very small numbers as com- 
pared with those found in adults dissected before oviposition. There 
were about 30 eggs in the ovaries of one and 50 in the other, which 
lived 45 and 47 hours, respectively. These adults had possibly en- 
gorged once, oviposited, and then developed the remaining eggs in 
the ovaries. 

In the condition of the ovaries of partly engorged adults these 
two points are worthy of notice: (1) No development of the ovaries 
took place unless the longevity of a specimen exceeded 40 hours; (2) 
stage 5 recurred in three cases. 

CONDITION OF THE OVARIES OF HALF-ENGORGED ADULTS. 

Five half -engorged (H — \-) adults were taken. The ovaries of two 
specimens contained eggs of the round type typical of stage 1. 
They lived for 7 and 21 hours, respectively. One adult contained 
ovaries filled with eggs of the typical oval shape (stage 3) in large 



TRANSFORMATIONS OF BUFFALO GNATS. 33 

numbers and dense white in color. This adult lived for 53 hours 
after engorgement. Two adults contained ovaries with fully de- 
veloped eggs in small numbers. In one adult there were 25 eggs in 
each ovary and in the other 18. Both these adults lived for only 4 
hours and 35 minutes after capture. This is probably a case of 
second feeding, because adults which lived for so short a period 
after engorgement could not have developed fully formed eggs in 
that time. The explanation of this condition is that they had prob- 
ably deposited only part of the full number of eggs at a previous 
oviposition. 

CONDITION OF THE OVAEIES OF WELL-EN GOEGED ADULTS. 

Twelve well-engorged (-| — | — |-) adults were taken on various dates, 
these specimens lived after capture from 7 to 47 hours. Only one 
specimen contained ovaries corresponding to stage 1. This specimen 
lived only seven hours and evidently had not had sufficient time in 
which to develop the ovaries. One specimen, which lived 17 hours, 
contained ovaries filled with eggs of stage 2, thus showing that the 
amount of development corresponds to the amount of engorgement 
and the requisite length of time after feeding. Six specimens, which 
lived from 17| hours to 24 hours 45 minutes, contained ovaries filled 
with eggs of the oval type typical of stage 3, again showing a con- 
stant amount of development in proportion to the previous engorge- 
ment and subsequent longevity. One specimen, which lived for 43 
hours, contained eggs of the oval type in a very small number, about 
20 in each ovary, with the remainder of the ovary apparently filled 
with the eggs of the round type (stage 1). One adult contained 
ovaries with fully developed eggs, but only 27 in each ovary. This 
specimen lived for 30 hours. Two adults contained ovaries filled 
with fully developed eggs, over 100 in each ovary. These lived for 
47 hours and evidently had the required factors, presumably a suffi- 
cient blood meal and sufficient time in which to digest, in order to 
develop the eggs within the ovaries. 

The foregoing data seem to show again that the development of 
the eggs within the ovaries is increased by the amount of food plus 
the length of the period of digestion. 

CONDITION OF THE OVAEIES OF FULLY ENGOEGED ADULTS. 

Thirty-one fully engorged (-| — 1 — | — [-) adults were taken from time 
to time and successfully dissected. They lived from 30 minutes to 
67-| hours. Six specimens contained ovaries corresponding to stage 
1. These lived from 30 minutes to 4 hours 35 minutes. Two adults, 
which lived 17 and 24 hours, respectively, contained ovaries with the 
eggs between stages 2 and 3. Six specimens contained ovaries with 
eggs typical of stage 3 in large numbers. These lived from 18 to 



34 

28j hours. One specimen which lived 23^ hours contained ovaries 
with only a small number of eggs, about 25 in each ovary. One 
adult which lived for 44 hours contained ovaries between the third 
and fourth stages, and showed the transition from stage 3 to 
stage 4 very clearly. Twelve adults contained ovaries filled with 
fully developed eggs (stage 4, PI. I, fig. 4), ranging in num- 
ber from 200 to 300. These adults lived from 30 to 67J hours. 
Two adults contained ovaries with eggs of stage 4. but in small 
numbers, about 50 in each ovary. They lived 48 and 56 hours, 
respectively, and possibly had developed the remainder of the eggs 
left within the ovary after a previous oviposition. One adult con- 
tained ovaries with eight fully developed eggs, and the remainder 
of the ovary filled with eggs corresponding to stage 3. This adult 
lived 34 hours and had presumably oviposited once, as is indicated 
by the presence of the eight fully developed eggs, and then devel- 
oped the remainder of the ovaries to stage 3. 

A comparative study of the ovaries of well-engorged (-j — | — \-) 
specimens shows that no adult which died before reaching a period 
of longevity of 30 hours after engorgement developed the eggs within 
the ovaries to full degree. On the other hand, with one exception, 
all adults which lived for 30 hours after engorgement developed the 
eggs within the ovaries to the fullest extent. The fully developed 
eggs within the ovaries were of the same shape as eggs freshly laid, 
and only a fraction smaller. 

THE APPARENT EFFECT OF A BLOOD MEAT LPON THE DEVELOPMENT OF THE OVAELES. 

In the studies which have been made of the ovaries of females of 
Simulium venustum under various conditions the following points 
are worthy of emphasis: (a) In all adults taken while oviposit- 
ing, apparently digested blood was found in the stomach, (h) Xo 
eggs within the ovaries developed to the fullest degree without en- 
gorgement and the requisite time in which to digest the blood meal. 

(c) The condition designated as stage 5 occurred both in adults 
which had just oviposited and also in adults which were taken on 
animals and killed at the time of capture. This condition (stage 5) 
seems to furnish strong evidence that adults feed again after oviposit- 
ing, as the majority of engorged adults showed the entire contents of 
the ovaries developed. In addition the exact cause of the similar 
condition found in adults which had just oviposited is known; 
namely, that a few fully developed eggs were left in the ovaries after 
oviposition and the remainder of the eggs were in a rudimentary 
condition apparently awaiting the necessary factors for development. 

(d) The males have reduced mouth parts and are not found engorg- 
ing on blood, indicating the acquisition of this habit by the females 
for a special purpose, as is the case with other blood-sucking Diptera. 



TRANSFORMATIONS OF BUFFALO GNATS. 35 



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38 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

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TRANSFORMATIONS OF BUFFALO GNATS. 39 

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v. 51, p. 659-668, 11 fig. Jena, 1909. 

A careful study of the structure of the mouth parts of Simulium. 
*Leth6, Julius. Hungarian Earthquakes and the Kolumbacs flies. In Nature, 

v. 21, p. 202, Jan., 1880. 

*Leebe, Johannes. Die larva von Simulia ornata Mg. (with 16 figs, in the 
text). In Zeitschrift fur Naturwissenschaften, Bd. 82, Heft 3-5, p. 
345-372. Leipzig, 1910. 

*Linn^:us, Caeolus. Lachesis Lapponica. Translated by J. E. Smith, v. 1, 
366 p. London, 1811. 

Pages 208-209. On attacks of Culex reptans in Pithoea. 



TRANSFORMATIONS OF BUFFALO GNATS. 41 

♦LiNKffitrs, Caroltjs. Flora Lapponica, 390 p., 12 pi. London, 1792. 

Pages 382-383. Description of Culex pulicaris=C. reptans=Simulium reptans. 
Known locally as " knort." 

*Loew, H. Diptera America? septentrionalis indigena. Centuria secunda. In 
Berlin. Ent. Ztschr., v. 6, p. 185-232. Berlin, 1862. 

Page 186. Simulium quadrivittatum, description of new species. 

*Lotjnsbury, Chakles P. Insect pests in South Africa. In Science in South 
Africa, p. 362-374, 1905. 

Simulium attacking poultry (brief mention), South Africa. 

*Luggek, Otto. Insects injurious in 1896. Univ. Minn. Agr. Expt. Sta. Ent. 
Div. Bui. 48, 270 p., 16 pi., 187 fig., 1896. 

Pages 198-208. Description of new species: Simulium minutum; S. irritatum; 
S. tribulatum=S. vittatum. 

*Lundbeck, Will. Diptera Groenlanclica. In Videnskabelige Meddelelser fra 

den naturhistoriske Forening i Kjobenhavn, p. 281-316, 5 fig., 1900. 
*Lundsteom, Cakl. Slaktet Simulium Latr. In Meddelanden af Societas pro 

Fauna et Flora Fennica, Heft 36, p. 103-104, 1910. 
*Lundstrom, Cael. Beitrage zur Kenntnis der Dipteren Finlands, VII. Mo- 

lusinidse (Simuliidse). In Acta Soc. pro Fauna et Flora Fennica, v. 34, 

no. 12, 24 p., 26 fig., Dec, 1911. 

A study of the male genitalia, showing the systematic value of the structures. 

*Lutz, A. Memorias do Instituto Oswaldo Cruz, t. 1, p. 124-146. Rio de 
Janeiro, 1909. 

Page 132, description of Simulium rubrithorax ; p. 133, S. scutistriatum ; 
p. 135, S. hirticosta ; p. 141, S. exiguum and S. varians ; p. 137, spp. n. Brazil. 
S. venustum var. infuscata. * 

*Lutz, A. Memorias do Instituto Oswaldo Cruz, t. 2, p. 213-267, 1910. 

Descriptions : S. infuscatum, p. 236 ; S. orbitale—nigrimanum Macq., p. 231 ; 
£. auristriatum, p. 245 ; S. incrustatam, p. 243 ; S. distinctum, p. 241 ; S. sub- 
nigrum, p. 239 ; S. subpallidum, p. 247 ; S. flavopubescens, p. 248 ; S. pruinosum, 
p. 250 ; S. simplicicolor, p. 251 ; S. minusculum, p. 253 ; S. rotulibranchium, p. 256 ; 
S. clavihranchium, p. 257 ; S. diversifurcatum, p. 258 ; S. arquifurcatum, S. bre- 
vibranchium, p. 260, spp. n. Brazil. 

*McBrtde, Sara J. The so-called web-worm of young trout. In Amer. Ent. and 

Bot, v. 2, no. 12, p. 365-366, Dec, 1870. 
*Macquart, M. Histoire Naturelle des Insectes, Dipteres. v. 1, p. 173-175, pi. 

4, fig. 15. Paris, 1834. 

Simulie. Simulium Latr. Description of genus and list of species. One colored 
figure of S. ornatum. 

*Malloch, J. R. One new genus of dipterous insects in the U. S. National 
Museum collection. In Proc U. S. Nat Mus., v. 43, no. 1945, p. 649-658, 
pi. 46, 1913. 

Page 649, pi. 46, fig. 67, Simulium bicoloratum; p. 650, fig. 8, S. bipunctatum; 
p. 650, fig. 9, S. toivnsendi; p. 652, S. nitidum. Locality, Peru. 

*Malloch, J. R. American black flies or buffalo gnats. U. S. Dept. Agr. 
Bur. Ent. Tech. Ser. no. 26, 71 p., 6 pi., 1914. 

Descriptions of new species : Prosimulium pleurale; Prosimulium mutatum; 
Parasimulium new genus ; Parasimulium furcatum; Simulium aureopunctatum ; 

5. hippovorum ; S. trivittatum ; S. bivittatum ; S. parnassum; S. arcticum ; S. jen- 
ningsi; S. clavipes; S. hunteri; S. hcematopotum ; S. forbesi. 

*Marlatt, C. L. Report of a trip to investigate buffalo gnats. In Insect Life, 
v. 2, no. 1, p. 7-11, July, 1889. 



42 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

*Mabshat,t,, P. New Zealand Diptera. In Trans, and Proc. N. Zeal. Inst., 
v. 28, art. 26, no. 3 (Simulidse), p. 310-311, pi. 14, June, 1896. 
Simulium australiense in New Zealand. 
*Mecznikow, Elias. Enibryologische Stuclien an Insecten. In Ztschr. Wiss. 
Zool., Bd. 16, Heft 4, p. 389-500, pi. 23, fig. 1-24. Leipzig, Dec. 6, 1866. 

A detailed study of the embryology of several insects. Aphis roses, Chironomus 
etc., including detailed account of the embryology of Simulium with excellent 
illustrations. 

*Megnin, J. P. Du role des mouches dans la propagation du charbon et autres 
affections virulentes. In Jour. Med. Yeter. Mil., t. 12, no. 8, p. 461--175. 
Paris, Jan., 1875. 

Simulium maculatum and £. dnereum transmitting diseases of cattle. 

*Megnin, J. P. Les Parasites et Les Maladies Parasitaires chez l'Homme, les 
Animaux Domestiques et les Animaux Sauvages -avec Lesquels ils Peuvent 
etre en Contact; Insectes, Arachnides, Crustac6s. 478 p., 26 pi., 63 fig. 
Paris, 1880. 

Pages 47-51. Mouches piquantes, Simulium, causing a psoriasis in the ears of 
horses, and also transmitting charbon. 

*Meigen, J. W. Versuch einer neuen Gattungs-Eintheilung cler europaischen 

zweiflugligen Insekten. In Magazin fur Insektenkunde herausgegeben von 

Karl Illiger, v. 2, p. 259-281. Braunschweig, 1803. 
*Meigen, J. W. Klassification und Bescbreibung der europaischen zweiflu- 

glichen Insecten, t. 1. Braunschweig, 1804. 
*Meijeee, J. C. H. de. Studien fiber Sudostasiatische Dipteren. In Tijdschr. 

Ent., v. 50, p. 196-264, pi. 5-6. 's-Gravenhage, Dec. 31, 1907. 

Pages 206-207. Description of Simulium nooile, male, new species from Java. 

*Meijeee, J. C. H. de. Blutsaugende Micro-Dipteren aus Niederllindisch Ostin- 
dien. In Tijdschr. Ent., v. 52, pi. 12, p. 191-204. 's-Gravenhage, Dec, 1909. 
Pages 202-203. Simulium nooile, female. Description. 

*Meineet, Fe. De eucephale Myggelarver. In K. Danske Vidensk. Selsk. Skr., 
ser. 6, v. 3, art. 4, p. 373-489, pi. 4, fig. 115-127, 1886. 

Pages 458—464. Anatomy of Simulium ornatum, with bibliography. 

*Meineet, Fe. Fluernes Munddele Tropi Dipterorum, 91 p., 6 pi. Kjobenhavn, 
1881. 

Pages 41-43. Simulium fuscipes ; S. reptans ; mouth parts of adults. 

*Meuniee, Feenand. Beitrag zur Fauna der Bibioniden, Simuliden, und 

Rhyphiden des Bernsteins. In Jahrb. Koniglich Preuss. Geol. Landesan- 

stalt und Bergakademie, Bd. 24, p. 391-404, pi. 17, fig. 8-11. Berlin, 1903. 

Pages 397-398. Descriptions of new fossil species, Simulium pulchella, S. affinis, 

S. importuna. 

*Miall, L. C. The Natural History of Aquatic Insects. 395 p., 116 fig. Lon- 
don, 1895. 

Pages 175-188. Simulium. 

*Mooee, H. W. B. Blood-sucking flies other than mosquitoes. In Jour. Boy. 
Agr. and Com. Soc. British Guiana, v. 1, ser. 3, p. 255-259, 1911. 
Simulium in British Guiana. Note on distribution, 

Mocsaey, Sandoe. A kolumbacsi legy. In Vasarnapi Ujsag, evfoly, 21 szam., 
p. 329-330. 1876. 

Die Fliege von Kolumbacz. 

*Mullee, Feitz. Larven von Mucken und Haarfluglern mit zweierlei abwech- 
selnd thatigen Athemwerkzeugen. In Ent. Nachr., v. 14, no. 18, p. 
273-277, Sept., 1888. 



TRANSFORMATIONS OP BUFFALO GNATS. 43 

♦New stead, Robert. Insects and other Arthropoda collected in the Congo Free 
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Mention of Simuliiim damnosum; 8. ornatum, habits and structural characters 
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♦Needham, J. C, and Betten, C. Aquatic insects in the Adirondack^. N. Y. 
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♦Niceville, Lionel de. Note on the " Potu " or " Pipsa " fly. In Indian Mus. 
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♦Nicholls, Lucius. Pellagra. " Sandfly Protozoon " versus " Zeist " theory. 
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♦Noel, Paul. La Mouche de Goluobatss. In Le Naturaliste, ser. 2, annee 28, 
no. 452, p. 13. Paris, Jan. 1, 1906. 

♦Osborn, Herbert. An old American account of the buffalo gnat. In Insect 
Life, v. 1, no. 7, p. 224-225, Jan., 1889. 

♦Osborn, Herbert. Insects affecting domestic animals. U. S. Dept. Agr., Biv. 
Ent., Bui. 5, n. s., 302 p., 5 pi., 170 fig., 1896. 
Pages 31-58. Simuliidae. 

♦Osten-Sacken, R. On the transformations of Simulium. In Amer. Ent., v. 2, 
no. 8, p. 229-231, fig. 145-147, June, 1870. 

♦Packard, A. S. History of the buffalo gnat. In Amer. Nat., v. 20, no. 7, p. 
650-651, 1886. 

Habits of Simulium larvae in North America. 

♦Packard, A. S. Our Common Insects. 225 p., 268 fig. Salem, 1873. 
Pages 72-73. The black fly. 

♦Philippi, R. A. Aufzlihlung der chilenischen Dipteren. In Verhandl. k. k. 
zool. bot. Gesell. Wien, Bd. 15, p. 595-782, 1865. 

Pages 633-635. Simulium fulvescens Blanch. Descriptions of new series, S. 
montanum, 8. pulchrum, 8. annulatum, 8. varipes, 8. chilense, 8. tarsatum. Chile. 

♦Planchon, J. E. Histoire d'une Larve Aquatique du Genre Simulium. 15 p. 

Montpellier, 1844. 
Pohl, J. E. Reise in das Innere von Brasilien. 2 volumes. Wien, 1832. 
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156-157. London, 1887. 
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Southern Peninsula of Michigan. In 12th Rpt. Mich. Acad. Sci., p. 77-78, 

1910. 
♦Riley, C. V. The death-web of young trout. In Amer. Ent. Bot., v. 2, no. 8, 

p. 227-228, fig. 143-144, June, 1870. 
♦Riley, C. V. Simulium piscicidium, n. sp. In Amer. Ent. Bot., v. 2, no. 12, p. 

367, December, 1870. 

Appendix to Sara J. McBride's article. 

♦Riley, C. V. On Simulium pictipes Hagen. In Amer. Nat., v. 15, no. 4, p. 

330, 1881. 
♦Riley, C. V. Simulium from Lake Superior. In Amer. Nat., v. 15, no. 11, p. 

916, 1881. 
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Agr. f. 1884, p. 340-345, pi. 9, fig. 1-3, 1884. 
Simulium ravages, etc. 



44 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

♦Riley, C. V. Report of the Entomologist. In Rpt. U. S. Coinr. Agr. f. 1886, p. 
459-592, 11 pi. 

Pages 461, 492, 517. The southern buffalo gnat, Simulium pecuarum, and the 
turkey gnat, S. meridionale n. sp. 

* Riley, C. V. A Virginia Simulium, called the " cholera gnat," also reply to 

letter suggesting remedy. In Insect Life, v. 1, no. 1, p. 14-15, July, 1888. 
*Riley, C. V. Buffalo gnats attacking man. In Insect Life, v. 1, no. 2, p. 60-61, 

Aug., 1888. 
*Riley, C. Y., and Howaed, L. O. Formula for a buffalo gnat application. Let- 
ter by Miss P. H. Skipwith. In Insect Life, v. 1. no. 5, p. 143, Nov., 1888. 

* Riley, C. V. Buffalo gnats on the Red River. (Letter by G. A. Frierson and 

reply.) In Insect Life, v. 1, no. 10, p. 313-314, April, 1889. 
*Riley, C. V., and Howard, L. O. A phase of buffalo gnat injury. In Insect 

Life, v. 2, no. 1, p. 2, July, 1889. 
Short note. 
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Frierson and reply.) In Insect Life, v. 4, nos. 3 and 4, p. 143-144, Not., 

1891. 
*Riley, C. Y., and Howaed, L. O. Great damage by buffalo gnats. In Insect 

Life, v. 4, p. 406, Aug., 1892. 
*Riley, C. Y., and Howaed, L. O. A new Simulium. In Insect Life, v. 5, p. 61, 

Sept., 1892. 

Note on Simulium occidentale Townsend. 
*Rlley, C. V., and Howaed, L. O. In Insect Life, v. 5, p. 81, Nov., 1892. 

Reference to Simulium occidentale and irrigation. 
*Robeets, S. R. Sambon's new theory of pellagra and its application to con- 
ditions in Georgia. In Jour. Amer. Med. Assoc, v. 56, no. 23, p. 1713-1715, 

June, 1911. 
*Robeets, S. R. The analogies of pellagra and the mosquito. In Amer. Jour. 

Med. Sci., v. 146, no. 2 (no. 497), p. 233-23S, Aug., 1913. 
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Mus. Hist. Nat., v. 11, no. 6, p. 424-427. Paris, 1905. 
*Roubaud, E. Simulies du Nippon Moyen. In Bui. Mus. Hist. Nat., y. 12, no. 1, 

p. 24-27, fig. 1-2. Paris, 1906. 
*RouBAUD, E. Apercus nouveaux, "morphologiques et biologiques, sur les 

Dipteres piqueurs du groupe des Simulies. In Compt. Rend. Acad. Sci., 

t. 143, p. 519-521. Paris, Oct. 8, 1906. 
*Roubattd, E. Sur deux types interressants de Simuliides de l'Afrique equa- 
toriale et des Nouvelles-Hebrides. In Bui. Mus. Hist. Nat., t. 12, no. 3, 

p. 140-143, 1 fig. Paris, 1906. 
*Roubaud, E. Insectes Dipteres. Simulies nouvelles ou peu connues. In Bui. 

Mus. Hist. Nat., v. 12, no. 7, p. 517-522. Paris, 1906. 
*Roubahd, E. Simulies nouvelles de l'Amerique du Sud. In Bui. Mus. Hist. 

Nat., v. 12, no. 2, p. 106-110. Paris, 1906. 
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*Rotjbattd, E. Note biologique sur un type adapte de Simulium reptans du 

Congo equatorial. In Ann. Inst. Pasteur, v. 21, p. 670-671. Paris, 1907. 
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Pathologie Exotique, t. 2, no. 7, p. 428-430. Paris, 1909. 

Description of a new species, Simulium escomeli, Peru. Also a definition of the 

subgenera Prosimulium and Eusimulium. 



TRANSFORMATIONS OF BUFFALO GNATS. 45 

*Rudow. Schadliche Mucken in der Mark. In Ent. Nachr., v. 4, no. 16, p. 
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Describes the attacks of Simuliiim maculata and 8. reptans upon horses and 
cattle throughout the valley of the Elbe. 

*Rudow. Die Kolumbaczer-Miicke. In Insektenborse, v. 20, no. 35, Aug., 1903. 

*Sambon, L. W. Progress report on the investigation of pellagra. In Jour. 
Trop. Med., v. 13, no. 18, p. 271-282 and no. 19, p. 287-300, Sept. and Oct., 
1910. 

That a minute blood-sucking fly of the genus Simulium is in all probability the 
agent by which pellagra is conveyed. 

*Sandeeson, B. D. Controlling the black fly in the White Mountains. In Jour. 
Econ. Ent., v. 3, no. 1, p. 27-29, pi. 2-3, Feb., 1910. 

*Say, Thomas. Entomology of North America, v. 2, p. 51, 1823. (Also in 
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*Schinee, J. R. Fauna Austriaca, v. 2, p. 363-369. Wien, 1864. 

Family Simulidse. 8imulia= Simulium Latr. Description of genus and list of 
species. 

*Schinee, J. R. Reise der oerterreichischen Fregatte Novara um die Erde. In 
Zoologischer Theil., Bd. 2, 385 p., 4 pi., 1868. 

Page 15. Simulium ornata and description of S. australensis n. sp. ; also men- 
tions number of described species to date. 

*Schiodte, J. G. Uebersicht der Band-Siisswasser-und Ufer-Anthropoden Gron- 
lands. In Berlin. Ent. Ztschr., v. 1, p. 152. Berlin, 1859. 
Antliata — Simulia vittata Zett. 1859. 

Schiodte, J. G. &. fuscipes. Kvaegmyggen. In Berlingske Tidende. May 16, 

1878. 

Schonbauek, J. A. Geschichte der Schadlichen Kolumbatczer Mucken im 
Bannat, als ein Beytrag zur Naturgeschichte von Ungarn. 100 p., 1 pi., 
Wien, 1795. 

*Schkottky, C. Drei neue blutsaugende Dipteren aus Paraguay. In Ztschr. 
Wiss. Insektenbiologie, Bd. 5, pt. 2, p. 61-63, 1909. 

Descriptions of new species : S. inexoraMle, 8. paranense, 8. paraguayense, 
Paraguay. 

*Shelfokd, R. Simulium and pellagra. In Nature, v. 85, no. 2141, p. 41. 
London, 1910. 

*Sktjse, F. A. A. Diptera of Australia, Simulidse and Bibionidse. In Proc. Linn. 
Soc. N. S. Wales, ser. 2, v. 3, pt. 4, p. 1363-1386, pi. 39, 1888. 
Page 1365, fig. 1. Description of 8. furiosum. Figure of wing. 
*Sktjse, F. A. A. Diptera of Australia. In Proc. Linn. Soc. N. S. Wales, ser. 2, 
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Page 632. SimuUum omatipes, new species, Australia. 

*Smith, J. B. A contribution toward a knowledge of the mouth parts of the 
Diptera. In Trans. Amer. Ent. Soc., v. 17, p. 319-339, 1890. 
Pages 323-326, fig. 4. Mouth parts of the buffalo gnat described and figured. 

*Speiseb, P. Zur Nomenclatur blutsaugender Dipteren Amerikas. In Insekten- 
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*St,egek, C. Groenlands Antliater. In Naturhistorisk Tidsskrift, 2 R., 1 Bind, 
p. 346-370. K0benhaven, 1844-1845. 
Page 357. Simulia vittata. 



46 BULLETIN 329, U. S. DEPARTMENT OF AGRICULTURE. 

*Steickland, E. H. Some parasites of Simulium larvre and their possible eco- 
nomic value. In Canad. Ent., v. 45, no. 12, p. 405-413, pi. 15, 1913. 

*Steickland, E. H. Some parasites of Simulium larvae and their effects on the 
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*Stkobl, Gabriel P. Dipterenfauna von Bosnien, Hercigovina und Dalmatia. 
In Wissenschaftliche Mittheilungen, Bosnien und der Hercegovina, Bd. 7, 
p. 552-670. Wien, 1900. 

Pages 648-649. Simulidae, description of S.argenteostriata n. sp. and 8. ornata 
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♦Stjmmees, S. L. M. Description of a new species of Simulium from the Siamese 
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*Taussig, Siegmund. Die Hundskrankheit (endemischer Magenkatarrh) in 
der Herzegowina. In Wiener Klin. Wchnschr., v. 18, no. 7, p. 163. Vienna, 
Feb. 16, 1905. 

Mention of Kriebemucken (Simuliidae). This name is applied here erroneously 
to the " Papadatsche fly " which is a species of Psychoda. 

*Tayloe, T. H. On the tracheal system of Simulium. In Trans. Ent. Soc. 
London f. 1902, p. 701-716, 8 fig. 

Teglas, Gaboe. A kolumbacsi legy Hunyad megy§ben. In Termeszettu- 
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*Theobald, Feed. V. An Account of British Flies, v. 1, 215 p., 44 fig., 4 pi. Lon- 
don, 1892. 

Pages 5, 15, 20, 165, 168. Simulidae — list of species and synonymy, Fig. 36, 8, 
reptans. 

♦Theobald, Feed. V. Report on a collection of mosquitoes and other flies from 
Equatorial East Africa and the Nile Provinces of Uganda. In Reports of 
the Sleeping Sickness Commision, Royal Society, no. 3, p. 33-42. London, 
1903. 

Tomosvaey Odon. Die Kolumbaczer Miicke. Im Auftrage des konigl. ung. 

Ministeriums fur Ackerbau, Industrie und Handel verfasst. 23 p., 1 pi. 
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*T6mosvaey, Odon. A Simulia-fajok babjanak lelekzoszervei. In Rovartani 
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Figure of pupal filaments of 8. columbaczense. 

Tomosvaey, Odon. Golubacka muha. In Glasnik Hrvatskoga Naravoslovnoga 
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*Townsend, C. H. T. A new Simulium from Southern New Mexico. In Psyche, 
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Description of new species, S. occidentals. 

*Townsend, C. H. T. On the correlation of habit on Nemocerous and Bra- 
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On the Simuliidae. (Danish.) 



TRANSFORMATIONS OF BUFFALO GNATS. 47 

*Veedat. Memoire pour servir a l'historie cles Simulies genre d'insectes de 

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Mention of " knott" (Simulia). 

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*Walkee, Feancts. List of the Specimens of Dipterous Insects in the Collec- 
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Pages 110-113. Simulium ; descriptions of new species, 8. decorum and S. 
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*Washbukn, F. L. Simuliiclse — Black flies, buffalo gnats. In Tenth Ann. Rpt. 
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*Webstee, F. M. The overflow of the Mississippi River and its effect upon the 
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48 

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